Wavelength selective switch (WSS) based multiplexing architecture

ABSTRACT

An apparatus may include a plurality of wavelength selective switches (WSSs). The apparatus may include a plurality of transmitters. The transmitters may transmit a plurality of super-channels. The apparatus may include a plurality of passive power splitters corresponding to the plurality of transmitters. The plurality of passive power splitters may receive the plurality of super-channels. The plurality of passive power splitters may generate a respective set of power-split super-channels for each super-channel of the plurality of super-channels. The plurality of passive power splitters may transmit each power-split super-channel of the respective set of power-split super-channels to a corresponding WSS of the plurality of WSSs. A WSS, of the plurality of WSSs, may receive a plurality of power-split super-channels, of the respective sets of power-split super-channels, from the plurality of passive power splitters. The WSS may selectively route a portion of the plurality of power-split super-channels toward a receiver.

BACKGROUND

Wavelength division multiplexed (WDM) optical communication systems(referred to as “WDM systems”) are systems in which multiple opticalsignals, each having a different wavelength, are combined onto a singleoptical fiber using an optical multiplexer circuit (referred to as a“multiplexer”). Such systems may include a transmitter circuit, such asa transmitter (Tx) photonic integrated circuit (PIC) having atransmitter component to provide a laser associated with eachwavelength, a modulator configured to modulate the output of the laser,and a multiplexer to combine each of the modulated outputs (e.g., toform a combined output or WDM signal), which may be collectivelyintegrated onto a common semiconductor substrate.

A WDM system may also include a receiver circuit, such as a receiver(Rx) PIC, having a photodiode, and an optical demultiplexer circuit(referred to as a “demultiplexer”) configured to receive the combinedoutput and demultiplex the combined output into individual opticalsignals.

A WDM system may also include a set of nodes (e.g., devices of the WDMsystem that may be utilized to route the multiple optical signals, addanother optical signal to the multiple optical signals, drop an opticalsignal from the multiple optical signals, or the like). For example, theWDM system may include a set of reconfigurable optical add-dropmultiplexers (ROADMs).

A wavelength of an optical signal output from the Tx PIC may be utilizedto transmit information at a fixed data rate. However, multiple opticalsignals may be combined into a unified channel that facilitatestransmission of information at a higher data rate. The multiple opticalsignals may be combined into one or more super-channels for routingthrough a network. A super-channel may refer to a set of channels that

SUMMARY

According to some possible implementations, an apparatus may include aplurality of wavelength selective switches (WSSs). The apparatus mayinclude a plurality of transmitters. The transmitters may transmit aplurality of super-channels. The apparatus may include a plurality ofpassive power splitters corresponding to the plurality of transmitters.The plurality of passive power splitters may receive the plurality ofsuper-channels. The plurality of passive power splitters may generate arespective set of power-split super-channels for each super-channel ofthe plurality of super-channels. The plurality of passive powersplitters may transmit each power-split super-channel of the respectiveset of power-split super-channels to a corresponding WSS of theplurality of WSSs. A WSS, of the plurality of WSSs, may receive aplurality of power-split super-channels, of the respective sets ofpower-split super-channels, from the plurality of passive powersplitters. The WSS may selectively route a portion of the plurality ofpower-split super-channels toward a receiver.

According to some possible implementations, a system may include aplurality of transmitters. The system may include a plurality of passivepower splitters. Each passive power splitter, of the plurality ofpassive power splitters, may be connected to a respective transmitter ofthe plurality of transmitters. The system may include a plurality ofwavelength selective switches. Each wavelength selective switch, of theplurality of wavelength selective switches, may be connected to theplurality of passive power splitters.

According to some possible implementations, a system may include areconfigurable optical add-drop multiplexer (ROADM). The ROADM mayinclude a set of passive power-splitters connected to a set of opticaltransmitters. The ROADM may include a first set of wavelength selectiveswitches. Each wavelength selective switch, of the first set ofwavelength selective switches, may be connected to the set of passivepower splitters. The ROADM may include a set of power combinersconnected to a set of optical receivers. The ROADM may include a secondset of wavelength selective switches. Each wavelength selective switch,of the second set of wavelength selective switches, may be connected tothe set of power combiners.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an overview of an example implementationdescribed herein;

FIGS. 2A-2E are diagrams of an example network in which systems and/ormethods, described herein, may be implemented;

FIGS. 3A and 3B are diagrams of example components of a reconfigurableoptical add-drop multiplexer shown in FIGS. 2A-2E, that may facilitaterouting of a super-channel;

FIG. 4 is another diagram of example components of the reconfigurableoptical add-drop multiplexer shown in FIGS. 2A-2E;

FIG. 5 is a flow chart of an example process for reducing wavelengthselective switch (WSS) filter-based impairment using comparative channelpre-emphasis; and

FIGS. 6A and 6B are diagrams of an example implementation relating tothe example process shown in FIG. 5;

FIG. 7 is a flow chart of an example process for reducing WSSfilter-based impairment using differentiated channel modulation formats;

FIGS. 8A and 8B are diagrams of an example implementation relating tothe example process shown in FIG. 7;

FIGS. 9A and 9B are flow charts of an example process for reducing WSSfilter-based impairment using multi-channel forward error correctionaveraging via an interleaving process;

FIGS. 10A-10D are diagrams of an example implementation relating to theexample process shown in FIGS. 9A and 9B;

FIG. 11 is a flow chart of an example process for reducing WSSfilter-based impairment using differentiated channel baud rates;

FIGS. 12A and 12B are diagrams of an example implementation relating tothe example process shown in FIG. 11;

FIG. 13 is a flow chart of an example process for reducing WSSfilter-based impairment using selective subcarrier adjustment;

FIGS. 14A and 14B are diagrams of an example implementation relating tothe example process shown in FIG. 13; and

FIG. 15 is a diagram of example components of one or more devicesdescribed herein.

DETAILED DESCRIPTION

The following detailed description of example implementations refers tothe accompanying drawings. The same reference numbers in differentdrawings may identify the same or similar elements.

An optical transmitter associated with a wavelength division multiplexed(WDM) optical communication system may transmit multiple optical signalsvia a single optical communication path using an optical multiplexercircuit. The optical transmitter may transmit one or more super-channelsthat include the multiple optical signals to a receive node, which mayinclude an optical receiver, of a network. Multiple optical transmittersmay be associated with a single transmit node and may transmit multiplesuper-channels for routing to multiple receive nodes.

A node may be referred to as “colorless” if ports of the node lack afixed wavelength assignment. In other words, tunabletransmitters/receivers have wavelength transparent access to any port ofthe multiplexing architecture. The node may be termed “directionless” ifchannels transmitted by the transmitter lack a fixed routing assignment(e.g., a first transmitter is configured to transmit to any of a set ofreconfigurable optical add-drop multiplexers (ROADMs) sharing opticallinks with the node, a second transmitter is configured to transmit toany of the set of ROADMs sharing optical links with the node, etc.). Inother words, transmitters/receivers of the node have non-blocking accessto ROADM output via the multiplexing architecture. The node may betermed “contentionless” if multiple ports of the multiplexing functionmay utilize the same wavelength. In other words, two or moretransmitters/receivers of the multiplexer may transmit/receive opticalsignals utilizing the same wavelength (e.g., to carry the sameinformation, to carry different information, or the like) to/from two ormore ports.

Utilizing a set of optical switches to facilitate routing multiplesuper-channels to multiple nodes may require expensive equipment and maylack the flexibility to handle changes to the network. Implementations,described herein, may utilize a set of passive splitters and wavelengthselective switches (WSSs) to provide a colorless, directionless, andcontentionless (CDC) broadcast multiplexing architecture.

A ROADM may include a WSS to allow a routing function for variousportions of the optical spectrum, such as to another ROADM. The WSS maysupport local addition of channels (add) and/or local dropping ofchannels (drop). The WSS may utilize routing to drop channels and anaddition and blocking functionality to add channels. For example, whenadding channels, a particular WSS filter pass-band may permit aparticular set of wavelengths to pass (add) without attenuation, and theparticular filter may attenuate other wavelengths present on an add portwhich are not desired. The use of a pass-band may impose a penalty onthe passed channels, such as because of a non-ideal shape of thepass-band, an undesired optical feature of the pass-band, or the like.The penalty may be an impairment of a portion of the passed channels,such as an impairment of an edge channel. An impaired optical signal mayincur bit errors during transmission (e.g., a quantity of bits of theoptical signal that are not received, that are not received correctly,or the like). A bit error rate above a threshold may result in anunacceptable quantity of information being lost from the optical signal.Similarly, another threshold performance metric may result indicate aninadequate signal that may be corrected by an impairment reductiontechnique, such as an optical performance monitor metric, a channelpower, an optical signal-to-noise ratio, or the like. A pass-band filtermay attenuate a first channel associated with a first set of wavelengthsmore than a second channel associated with a second set of wavelengths,resulting in different bit error rates for the first channel and thesecond channel of a super-channel. Concentrating bit errors in aparticular channel of a set of channels may result in degraded networkperformance. Implementations, described herein, may utilize a set oftechniques to reduce the impact of WSS filter-based impairment. In someimplementations, the set of techniques may reduce a bit error rate,reduce a differential between a first bit error rate of a first channeland a second bit error rate of a second channel, or the like.

FIG. 1 is a diagram of an overview of an example implementation 100described herein. As shown in FIG. 1, a node (e.g., a ROADM) may includea set of transmitter (Tx) photonic integrated circuits (PICs) (e.g., TxPICs (1) through (N)) that may transmit a corresponding set of opticalsignals (e.g., optical signals (1) through (N)). Each optical signal mayinclude one or more super-channels. Each super-channel may be comprisedof a set of channels and each channel may be comprised of a set ofsubcarriers. A set of passive power splitters (e.g., passive powersplitters (1) through (N)) corresponding to the set of Tx PICs mayreceive the set of optical signals. For example, passive power splitter(1) may receive optical signal (1) from Tx PIC (1). Similarly, passivepower splitter (N) may receive optical signal (N) from Tx PIC (N). Aparticular passive power splitter may power-split a particular opticalsignal received from a particular Tx PIC into a particular quantity ofpower-split portions for routing to a set of WSSs. For example, when mWSSs are associated with passive power splitter (1), passive powersplitter (1) may power-split optical signal (1) into m power-splitportions (e.g., each power split portion resembling optical signal (1)but having approximately one mth of the power of optical signal (1)).Similarly, passive power splitter (N) may power-split optical signal (N)into m power-split portions.

As further shown in FIG. 1, the particular power splitter may transmitthe set of power-split portions to the set of WSSs. For example, passivepower splitter (1) may provide a first one-mth power-split portion toWSS (1), a second one-mth power-split portion to WSS (2), etc. A WSS mayutilize a set of filters to selectively route optical signals receivedfrom the set of passive power splitters to a set of other ROADMS (e.g.,other nodes of an optical network). For example, WSS (1) may route areceived one-mth power-split portion of optical signal (1) toward areceiver associated with another ROADM. Additionally, or alternatively,a particular WSS may route multiple received optical signals.Additionally or alternatively, a particular optical signal may be routedto multiple receive nodes via multiple WSSs.

In this way, a set of passive power splitters connected to a set of WSSsassociated may facilitate CDC broadcast multiplexing.

FIGS. 2A-2E are diagrams of an example environment 200 in which systemsand/or methods, described herein, may be implemented. As shown in FIG.2A, environment 200 may include a network management device 210, and anoptical network 220, which may include a set of network devices 230-1through 230-N(N≧1) (hereinafter referred to individually as “networkdevice 230,” and collectively as “network devices 230”). Devices ofenvironment 200 may interconnect via wired connections, wirelessconnections, or a combination of wired and wireless connections.

Network management device 210 may include one or more devices capable ofreceiving, generating, storing, processing, and/or providing informationassociated with a network (e.g., optical network 220). For example,network management device 210 may include a computing device, such as aserver, a controller, an optical performance monitor device, or asimilar type of device. Network management device 210 may assist a userin modeling, planning, and/or controlling a network, such as opticalnetwork 220. For example, network management device 210 may assist inmodeling and/or planning an optical network configuration, which mayinclude quantities, locations, capacities, parameters, and/orconfigurations of network devices 230. In some implementations, networkmanagement device 210 may cause a technique for reducing WSSfilter-based-impairment to be applied to one or more network devices230. In some implementations, network management device 210 may causeone or more optical signals to be routed via optical network 220. Insome implementations, network management device 210 may be a distributeddevice associated with one or more network devices 230. In someimplementations, network management device 210 may be a component ofnetwork device 230 (e.g., a controller, a transmitter, a receiver, orthe like). In some implementations, network management device 210 may beimplemented as a processor, a microprocessor, an application-specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), orthe like. In some implementations, network management device 210 mayrefer to one or more testing, simulation, and/or configuration devicesassociated with designing or operating an optical network 220.

Optical network 220 may include any type of network that uses light as atransmission medium. For example, optical network 220 may include afiber-optic based network, an optical transport network, alight-emitting diode network, a laser diode network, an infrarednetwork, and/or a combination of these or other types of opticalnetworks. Optical network 220 may include one or more optical routes(e.g., optical lightpaths) that may specify a route along which light iscarried (e.g., using one or more optical links) between two or morenetwork devices 230 (e.g., via an optical link). An optical link mayinclude an optical fiber, an optical control channel, an optical datachannel, or the like, and may carry an optical channel (e.g., a signalassociated with a particular wavelength of light that may include a setof optical subcarriers that subdivide the optical channel), an opticalsuper-channel (e.g., a set of optical signals), a super-channel set, anoptical carrier set, a set of spectral slices, or the like.

Network device 230 may include one or more devices capable of receiving,generating, storing, processing, and/or providing data carried by anoptical signal via an optical link. For example, network device 230 mayinclude one or more optical data processing and/or optical traffictransfer devices, such as an optical amplifier (e.g., a doped fiberamplifier, an erbium doped fiber amplifier, a Raman amplifier, etc.), anoptical add-drop multiplexer (OADM) (e.g., a reconfigurable opticaladd-drop multiplexer (ROADM), a flexibly reconfigurable optical add-dropmultiplexer (FROADM), etc.), an optical source device (e.g., a lasersource), an optical destination device (e.g., a laser sink), an opticalmultiplexer, an optical demultiplexer, an optical transmitter, anoptical receiver, an optical transceiver, a photonic integrated circuit(PIC), an integrated optical circuit, a wavelength selective switch(WSS), a power splitter (e.g., a passive power splitter, an active powersplitter, or the like), a power combiner, or the like. In someimplementations, network device 230 may include one or more opticalcomponents. Network device 230 may process and/or transmit an opticalsignal (e.g., to another network device 230 via an optical link) todeliver the optical signal through optical network 220.

The number and arrangement of devices and networks shown in FIG. 2A areprovided as an example. In practice, there may be additional devicesand/or networks, fewer devices and/or networks, different devices and/ornetworks, or differently arranged devices and/or networks than thoseshown in FIG. 2A. Furthermore, two or more devices shown in FIG. 2A maybe implemented within a single device, or a single device shown in FIG.2A may be implemented as multiple, distributed devices. Additionally, oralternatively, a set of devices (e.g., one or more devices) ofenvironment 200 may perform one or more functions described as beingperformed by another set of devices of environment 200.

FIG. 2B is a diagram of example devices of optical network 220 that maybe designed, monitored, and/or configured according to implementationsdescribed herein. One or more devices shown in FIG. 2B may operatewithin optical network 220, and may correspond to one or more networkdevices 230 and/or one or more optical components of a network device230. As shown, optical network 220 may include a set of opticaltransmitter devices 240-1 through 240-M (M≧1) (hereinafter referred toindividually as “Tx device 240,” and collectively as “Tx devices 240”),a set of super-channels 245-1 through 245-M (M≧1) (hereinafter referredto individually as “super-channel 245,” and collectively as“super-channels 245”), a multiplexer (“MUX”) 250, a set of ROADMs 260-1through 260-L (L≧1) (hereinafter referred to individually as “ROADM260,” and collectively as “ROADMs 260”), a demultiplexer (“DEMUX”) 270,and one or more optical receiver devices 275-1 through 275-K (K≧1)(hereinafter referred to individually as “Rx device 275,” andcollectively as “Rx devices 275”).

Tx device 240 may include, for example, an optical transmitter and/or anoptical transceiver that generates an optical signal. For example, Txdevice 240 may include one or more integrated circuits, such as atransmitter photonic integrated circuit (PIC), an application specificintegrated circuit (ASIC), or the like. In some implementations, Txdevice 240 may include a laser associated with each wavelength, adigital signal processor to process digital signals, a digital-to-analogconverter to convert the digital signals to analog signals, a modulatorto modulate the output of the laser, and/or a multiplexer to combineeach of the modulated outputs (e.g., to form a combined output or WDMsignal). One or more optical signals may be carried as super-channel245. In some implementations, a single Tx device 240 may be associatedwith a single super-channel 245. In some implementations, a single Txdevice 240 may be associated with multiple super-channels 245, ormultiple Tx devices 240 may be associated with a single super-channel245. In some implementations, Tx device 240 may include a forward errorcorrection (FEC) encoder, a FEC interleaver, or the like. In someimplementations, Tx device 240 may correspond to and/or include one ormore components described herein with regards to FIG. 6A, FIG. 8A, FIG.10A, FIG. 12A, and/or FIG. 14A.

Super-channel 245 may include multiple channels (e.g., optical signals)multiplexed together using wavelength-division multiplexing to increasetransmission capacity. Various quantities of channels may be combinedinto super-channels using various modulation formats to create differentsuper-channel types having different characteristics. Various quantitiesof subcarriers may be combined into channels using various modulationformats. In some implementations, an optical link may include asuper-channel set. A super-channel set may include multiplesuper-channels multiplexed together using wavelength-divisionmultiplexing to increase transmission capacity. Examples ofsuper-channels 245 will be described herein with respect to FIG. 2C.

Multiplexer 250 may include, for example, an optical multiplexer (e.g.,a power multiplexer, a WSS-based multiplexer, a multi-cast multiplexer,or the like) that combines multiple input super-channels 245 fortransmission via an output fiber). For example, multiplexer 250 maycombine super-channels 245-1 through 245-M, and may provide the combinedsuper-channels 245 to ROADM 260 via an optical link (e.g., a fiber).

ROADM 260 may include, for example, an OADM, a ROADM, a FROADM, or thelike. ROADM 260 may multiplex, de-multiplex, add, drop, and/or routemultiple super-channels 245 into and/or out of a fiber (e.g., a singlemode fiber). As illustrated, a particular ROADM 260, of the set ofROADMs 260, may drop super-channel 245-1 from a fiber, and may allowsuper-channels 245-2 through 245-M to continue propagating toward Rxdevice 275 and/or another ROADM 260. Dropped super-channel 245-1 may beprovided to a device (not shown) that may demodulate and/or otherwiseprocess super-channel 245-1 to output the data stream carried bysuper-channel 245-1. As further shown, ROADM 260 may add super-channel245-1′ to the fiber. Super-channel 245-1′ and super-channels 245-2through 245-M may propagate to demultiplexer 270 and/or another ROADM260. A network including multiple ROADMs 260 is described in more detailherein in connection with FIG. 2D and FIG. 2E.

Demultiplexer 270 may include, for example, an optical de-multiplexer(e.g., a power demultiplexer, a WSS-based demultiplexer, or the like)that separates multiple super-channels 245 carried over an input fiber.For example, demultiplexer 270 may separate super-channels 245-1′ andsuper-channels 245-2 through 245-M, and may provide each super-channel245 to a corresponding Rx device 275.

Rx device 275 may include, for example, an optical receiver and/or anoptical transceiver that receives an optical signal. For example, Rxdevice 275 may include one or more integrated circuits, such as areceiver PIC, an ASIC, or the like. In some implementations, Rx device275 may include a demultiplexer to receive combined output anddemultiplex the combined output into individual optical signals, aphotodetector to convert an optical signal to a voltage signal, ananalog-to-digital converter to convert voltage signals to digitalsignals, and/or a digital signal processor to process the digitalsignals. One or more optical signals may be received by Rx device 275via super-channel 245. Rx device 275 may convert a super-channel 245into one or more electrical signals, which may be processed to outputinformation associated with each data stream carried by an opticalchannel included in super-channel 245. In some implementations, a singleRx device 275 may be associated with a single super-channel 245. In someimplementations, a single Rx device 275 may be associated with multiplesuper-channels 245, or multiple Rx devices 275 may be associated with asingle super-channel 245. In some implementations, Rx device 275 mayinclude a FEC decoder, a FEC de-interleaver, or the like.

One or more devices shown in FIG. 2B may correspond to a single networkdevice 230. In some implementations, a combination of devices shown inFIG. 2B correspond to a single network device 230. For example, Txdevices 240-1 through 240-M and multiplexer 250 may correspond to asingle network device 230. As another example, Rx devices 275-1 through275-K and demultiplexer 270 may correspond to a single network device230.

The number and arrangement of devices shown in FIG. 2B are provided asan example. In practice, there may be additional devices, fewer devices,different devices, or differently arranged devices, included in opticalnetwork 220, than those shown in FIG. 2B. Furthermore, two or moredevices shown in FIG. 2B may be implemented within a single device, or asingle device shown in FIG. 2B may be implemented as multiple,distributed devices. Additionally, or alternatively, a set of devicesshown in FIG. 2B may perform one or more functions described as beingperformed by another set of devices shown in FIG. 2B.

FIG. 2C is a diagram of example super-channels 245 that may be monitoredand/or configured according to implementations described herein. Asuper-channel, as used herein, may refer to multiple optical channelsthat are simultaneously transported over the same optical waveguide(e.g., a single mode optical fiber). Each optical channel included in asuper-channel may be associated with a particular optical wavelength (orset of optical wavelengths). Each optical channel included in asuper-channel may be associated with multiple subcarriers. Eachsubcarrier may be associated with a particular optical wavelength. Themultiple optical channels may be combined to create a super-channelusing wavelength division multiplexing. In some implementations, eachoptical channel may be modulated to carry an optical signal.

An example frequency and/or wavelength spectrum associated withsuper-channels 245 is illustrated in FIG. 2C. In some implementations,the frequency and/or wavelength spectrum may be associated with aparticular optical spectrum (e.g., C Band, C+Band, etc.). Asillustrated, super-channel 245-1 may include multiple optical channels280, each of which corresponds to a wavelength λ (e.g., λ1, λ2, throughλ10) within a first wavelength band. Similarly, super-channel 245-M mayinclude multiple optical channels 280, each of which corresponds to awavelength λ (e.g., λY-X through λY) within a second wavelength band.The quantity of illustrated optical channels 280 per super-channel 245is provided for explanatory purposes. In practice, super-channel 245 mayinclude any quantity of optical channels 280.

Optical channel 280 may be associated with a particular frequency and/orwavelength of light. In some implementations, optical channel 280 may beassociated with a frequency and/or wavelength at which the intensity oflight carried by optical channel 280 is strongest (e.g., a peakintensity, illustrated by the peaks on each optical channel 280). Insome implementations, optical channel 280 may be associated with a setof frequencies and/or a set of wavelengths centered at a centralfrequency and/or wavelength. The intensity of light at the frequenciesand/or wavelengths around the central frequency and/or wavelength may beweaker than the intensity of light at the central frequency and/orwavelength, as illustrated.

In some implementations, the spacing between adjacent wavelengths (e.g.,λ1 and λ2) may be equal to or substantially equal to a bandwidth (or bitrate) associated with a data stream carried by optical channel 280. Forexample, assume each optical channel 280 included in super-channel 245-1(e.g., λ1 through λ10) is associated with a 50 Gigabit per second(“Gbps”) data stream. In this example, super-channel 265-1 may have acollective data rate of 500 Gbps (e.g., 50 Gbps×10). In someimplementations, the collective data rate of super-channel 245 may begreater than or equal to 100 Gbps. Additionally, or alternatively, thespacing between adjacent wavelengths may be non-uniform, and may varywithin a particular super-channel band (e.g., super-channel 245-1). Insome implementations, optical channels 280 included in super-channel 245may be non-adjacent (e.g., may be associated with non-adjacentwavelengths in an optical spectrum).

Each super-channel 245 may be provisioned in optical network 220 as oneoptical channel and/or as an individual optical channel. Provisioning ofan optical channel may include designating a route for the opticalchannel through optical network 220. For example, an optical channel maybe provisioned to be transmitted via a set of network devices 230.Provisioning may be referred to as “allocating” and/or “allocation”herein.

As shown in FIG. 2D, optical network 220 may include a set of ROADMs260-1 through 260-5 (e.g., nodes of optical network 220) that mayfacilitate communication via optical network 220. Network device 230(e.g., Tx device 240, Rx device 275, or the like) may output/receive aset of super-channels 245 to/from ROADM 260-1 via optical link 285(e.g., an optical fiber). ROADM 260-1 may be connected via a firstoptical link 285 to ROADM 260-2 and via a second optical link 285 toROADM 260-5. Furthermore, for example, ROADM 260-2 may be connected viaa first optical link 285 to ROADM 260-3 and via a second optical link285 to ROADM 260-4. The set of super-channels 245 may include a set ofindividually routable super-channels 245-1 through 245-3. In someimplementations, ROADM 260 may perform first node routing. For example,when ROADM 260 is as a first node of optical network 220 that receivesthe set of super-channels 245 from a source of the set of super-channels245, ROADM 260 may route the set of super-channels 245 to differentROADMs 260. In other words, a particular ROADM 260 that receives theindividual super-channels 245 from a source of the individualsuper-channels 245 (e.g., Tx device 240), performs routing for theindividual super-channels 245 to a set of other ROADMs 260. For example,ROADM 260-1 may receive super-channel 245-1 from network device 230(e.g., Tx device 240) and may route super-channel 245-1 to ROADM 260-5and may receive super-channel 245-2 from network device 230 (e.g., Txdevice 240) and may route super-channel 245-2 to ROADM 260-2. In someimplementations, ROADM 260-1 may perform first node routing using a setof WSSs, a set of passive power-splitters, a set of passivepower-combiners, or the like, configured to independently route one ormore super-channels 245 of a set of super-channel 245, as describedherein in connection with FIGS. 3A-3B and FIG. 4.

As shown in FIG. 2E, optical network 220 may include a networkconfiguration utilizing multiple ROADMs 260 (e.g., nodes of opticalnetwork 220) to route super-channel 245 from a source of super-channel245 to a destination for super-channel 245. For example, ROADM 260-1 mayreceive super-channel 245 and may route super-channel 245 via ROADM260-2, ROADM 260-3, and ROADM 260-4 to ROADM 260-5. Additionally, oralternatively, ROADM 260-1 may route super-channel 245 via ROADM 260-8and ROADM 260-9 to ROADM 260-5. In some implementations, ROADM 260-1 mayselect a routing path for super-channel 245 based on a distanceassociated with the routing path, a quantity of nodes traversed via therouting path, a wavelength availability associated with the routingpath, or the like. FIG. 2E is provided as an example of optical network220. Optical network 220 may include a different quantity of ROADMs 260,a different set of paths connecting a set of ROADMs 260, a different setof network devices 230, or the like.

FIGS. 3A and 3B are diagrams of components of ROADM 260 shown in opticalnetwork 220 of FIG. 2B. As shown in FIG. 3A, ROADM 260 may include a setof Tx devices 240-1 through 240-N(N≧1), a set of passive power splitters310-1 through 310-N(N≧1) (hereinafter referred to individually as“passive power splitter 310,” and collectively as “passive powersplitters 310”), and a set of wavelength selective switches (WSSs) 320-1through 320-M (M≧1) (hereinafter referred to individually as “WSS 320,”and collectively as “WSS 320”).

Passive power splitter 310 may include, for example, a power splitterthat is configured to receive an optical signal and route a set ofpower-split portions of the optical signal to a set of other networkdevices 230 (e.g., a set of WSSs 320). In some implementations, passivepower splitter 310 may generate a quantity of power-split portions ofthe optical signal corresponding to a quantity of WSSs 320. In someimplementations, each power-split portion of the optical signal mayrepresent the information of the optical signal with a transmissionpower proportional to the quantity of power-split portions andtransmission power of the optical signal. In some implementations,passive power splitter 310 may include a rack-mounted passive splitter,a non-rack-mounted passive splitter, or the like.

WSS 320 may include, for example, a set of wavelength selective switchesassociated with routing an optical signal. For example, a particular WSS320 may be associated with receiving a set of optical signals fromanother ROADM 260 and selectively routing a portion of the set ofoptical signals to a set of other WSSs 320 and/or a set of Rx devices275. Additionally, or alternatively, a particular WSS 320 may beassociated with receiving another set of optical signals from a set ofother WSSs 320 and/or a set of Tx devices 240 and selectively routing aportion of the other set of optical signals to the other ROADM 260. Insome implementations, WSS 320 may be connected to an amplifier devicethat is configured to increase the power associated with a power-splitportion of a particular super-channel 245 that is received by WSS 320.In some implementations, WSS 320 may selectively route a portion of oneor more received super-channels 245 to another WSS 320.

As further shown in FIG. 3A, a set of Tx devices 240-1 through 240-N maytransmit a set of super-channels 245-1 through 245-N to the set ofpassive power splitters 310-1 through 310-N. For example, Tx device240-1 may transmit super-channel 245-1 to passive power splitter 310-1.In some implementations, each passive power splitter 310, of the set ofpassive power splitters 310, may provide respective power-split portionsof the set of super-channels 245 to each WSS 320 of the set of WSSs 320.For example, passive power splitter 310-1 may provide a first powersplit portion of super-channel 245-1 (e.g., a power split portion thatis associated with information of super-channel 245-1 and aproportionally reduced transmission power) to WSS 320-1 (e.g.,super-channel 245-1 (1)), a second power-split portion of super-channel245-1 to WSS 320-2, an mth power split-portion of super-channel 245-1 toWSS 320-M (e.g., super-channel 245-1 (M)), etc. In other words, each WSS320 receives a passively power-split copy of each super-channel 245 ofthe set of super-channels 245.

In this way, multiple Tx devices 240, of ROADM 260, may direct anoptical signal to multiple WSSs 320, of the ROADM 260, associated withrouting the optical signal to respective other ROADMs 260.

Although FIG. 3A is described in terms of super-channels beingtransmitted by Tx device 240, FIG. 3A may also refer to a set ofsuper-channels, a set of channels, a set of subcarriers, or the likebeing transmitted by Tx device 240.

As shown in FIG. 3B, ROADM 260 may include a set of Rx devices 275-1through 275-Q (Q≧1), a set of WSS 320-R through 320-P (P≧1), and a setof power combiners 330-1 through 330-Q (Q≧1) (hereinafter referred toindividually as “power combiner 330,” and collectively as “powercombiners 330”).

Power combiner 330 may include, for example, a power combiner that isconfigured to combine multiple optical signals and route the multipleoptical signals to Rx device 275. In some implementations, powercombiner 330 may include an active power combiner, a passive powercombiner, or the like. In some implementations, power combiner 330 mayinclude another type of combiner, such as a WSS, an arrayed waveguidegrating (AWG), a fixed passive spectral filter, or the like.

As further shown in FIG. 3B, the set of WSSs 320-R through 320-P mayreceive a set of optical signals (e.g., from a set of network devices230, from a set of other WSSs 320 associated with a set of other ROADMs260, or the like) that may include one or more super-channels 245. Insome implementations, a particular WSS 320 may be associated with a setof optical links 285. For example WSS 320-R may be associated withoptical link 285-R (1) to power combiner 330-1, optical link 285-R (Q)to power combiner 330-Q, etc. Similarly, WSS 320-P may be associatedwith optical link 285-P (1) to power combiner 330-1, optical link 285-P(Q) to passive power combiner 330-P, etc. In some implementations, WSS320 may selectively route one or more portions of the set of opticalsignals to one or more power combiners 330, of the set of powercombiners 330, via one or more optical links 285. For example, WSS 320-Rmay, when receiving an optical signal that includes super-channel 245-R,route a portion of super-channel 245-R (e.g., super-channel 245-R (1))via optical link 285-R (1). In some implementations, a particular powercombiner 330 may receive multiple portions of multiple super-channels285 and may combine and route the multiple portions to a particular Rxdevice 275. For example, power combiner 330-1 may receive super-channel245-R (1) and super-channel 245-P (1) and may combine into super-channel245-1′ for routing to Rx device 275-1.

In this way, multiple Rx devices 275, of ROADM 260, may selectivelyreceive a portion of multiple optical signals received by multiple WSSs320 of ROADM 260.

Although FIG. 3B is described in terms of super-channels being receivedby Rx device 275, FIG. 3B may also refer to a set of super-channels, aset of channels, a set of subcarriers, or the like being received by Rxdevice 275.

The number and arrangement of components shown in FIGS. 3A and 3B areprovided as an example. In practice, ROADM 260 may include additionalcomponents, fewer components, different components, or differentlyarranged components than those shown in FIGS. 3A and 3B. Additionally,or alternatively, a set of components shown in FIGS. 3A and 3B mayperform one or more functions described herein as being performed byanother set of components shown in FIGS. 3A and 3B.

FIG. 4 is a diagram of an example implementation of ROADM 260 shown inFIG. 2B and FIGS. 3A and 3B. As shown in FIG. 4, ROADM 260 includesROADM degree 410-1 and ROADM degree 410-2, a set of Tx devices 240-1 and240-2, which are associated with a corresponding set of passive powersplitters 310-1 and 310-2, and a set of Rx devices 275-1 and 275-2,which are associated with a corresponding set of power combiners 330-1and 330-2. ROADM degree 410-1 includes WSS 320-1, which is associatedwith receiving super-channel 245-1 from first ROADM 260, and WSS 320-2,which is associated with providing super-channel 245-2 to first ROADM260. ROADM degree 410-2 includes WSS 320-3, which is associated withreceiving super-channel 245-3 from second ROADM 260, and WSS 320-4,which is associated with providing super-channel 245-4 to second ROADM260.

WSS 320-1 receives super-channel 245-1 and selectively provides aportion of super-channel 245-1 to power combiner 330-1, power combiner330-2, and/or WSS 320-4. For example, WSS 320-1 may provide a first setof channels of super-channel 245-1 to power combiner 330-1, a second setof channels of super-channel 245-1 to power combiner 330-2, and a thirdset of channels of super-channel 245-1 to WSS 320-4. In someimplementations, the first set of channels, the second set of channels,and/or the third set of channels may be the same set of channels, adifferent set of channels, or a combination of the same and differentsets of channels. Similarly, WSS 320-3 may receive super-channel 245-3and may selectively provide a portion of super-channel 245-3 to powercombiner 330-1, power combiner 330-2, and/or WSS 320-2.

Power combiner 330-1 may receive a portion of super-channel 245-1 fromWSS 320-1 and a portion of super-channel 245-3 from WSS 320-3. Powercombiner 330-1 may power combine the portion of super-channel 245-1 andsuper-channel 245-2, to generate a power-combined optical signal. Powercombiner 330-1 may provide the power-combined optical signal to Rxdevice 275-1 for detection, processing, or the like. Similarly, powercombiner 330-2 may provide a portion of super-channel 245-1, receivedfrom WSS 320-1, and a portion of super-channel 245-3, received from WSS320-3, to Rx device 275-2 for detection, processing, or the like. Inthis way, WSS 320 may route a particular super-channel 245 to anotherWSS 320 for transmission to another ROADM 260 or to an Rx device 275, ofa set of Rx devices 275, for detection, processing, or the like, therebyfacilitating CDC broadcast multiplexing.

Passive power splitter 310-1 may provide a first power-split portion ofan optical signal, received from Tx device 240-1, to WSS 320-2 and asecond power-split portion of the optical signal to WSS 320-4.Similarly, passive power splitter 310-2 may provide a first power-splitportion of another optical signal, received from Tx device 240-2, to WSS320-2 and a second power-split portion of the other optical signal toWSS 320-4.

WSS 320-2 may receive a set of optical signals from passive powersplitter 310-1, passive power splitter 310-2, and/or WSS 320-3. WSS320-2 may selectively route a portion of or all of the set of opticalsignals as super-channel 245-2 to first ROADM 260. Similarly, WSS 320-4may receive a set of optical signals from passive power splitter 310-1,passive power splitter 310-2, and/or WSS 320-1. WSS 320-4 mayselectively route a portion of or all of the set of optical signals assuper-channel 245-4 to second ROADM 260. In this way, WSS 320 mayselectively route a set of optical signals received from a set of othernetwork devices 230 (e.g., passive power splitter 310, another WSS 320,or the like) to another ROADM 260, thereby facilitating CDC broadcastmultiplexing.

While FIG. 4 shows ROADM 260 as including a particular quantity andarrangement of components, in some implementations, ROADM 260 mayinclude additional components, fewer components, different components,or differently arranged components.

FIG. 5 is a flow chart of an example process 500 for reducing WSSfilter-based impairment using comparative channel pre-emphasis. In someimplementations, one or more process blocks of FIG. 5 may be performedby network management device 210. In some implementations, one or moreprocess blocks of FIG. 5 may be performed by another component or a setof components separate from or including network management device 210,such as network device 230 (e.g., Tx device 240, MUX 250, ROADM 260,DEMUX 270, Rx device 275) or the like.

As shown in FIG. 5, process 500 may include monitoring a set of channelsto determine a bit error rate (block 510). For example, networkmanagement device 210 may monitor the set of channels to determine thebit error rate. A bit error rate may refer to a ratio of received bitsof a data stream that have been altered and/or dropped (e.g., due tonoise, interference, distortion, etc.) as compared to a total quantityof transferred bits. For example, when a super-channel is transmitted byTx device 240 to WSS 320 (e.g., via passive power splitter 310) fortransmission to another ROADM 260, the super-channel may be filtered(e.g., by a pass-band filter associated WSS 320). In someimplementations, the set of channels may include multiple channels withdifferent sets of wavelengths (e.g., sets of wavelength ranges). In someimplementations, network management device 210 may monitor the set ofchannels to determine another signal quality factor, such as a signal tonoise ratio, a Q-factor, or the like.

The pass-band filter (sometimes referred to as a “band-pass filter”) maypermit a first set of frequencies to pass through with a first quantityattenuation and may permit a second set of frequencies to pass throughwith a second quantity of attenuation. For example, when thesuper-channel is filtered by the pass-band filter, frequencies (e.g.,corresponding to a set of wavelengths) associated with a first set ofchannels may be passed through with a lesser attenuation compared withfrequencies associated with a second set of channels. In someimplementations, the pass-band filter may attenuate edge channels morethan interior channels. An interior channel may refer to a channel forwhich the frequency range is surrounded by a pair of edge channels. Forexample, when a super-channel includes five sequential channels withnon-overlapping frequency ranges, the super-channel may include two edgechannels and three interior channels.

The bit error rate may correspond to an attenuation of a channel by thepass-band filter, in some implementations. For example, a first channel,that undergoes greater attenuation by the pass-band filter than a secondchannel, may be associated with a higher bit error rate than the secondchannel. In some implementations, the bit error rate may correspond totransmission power after attenuation. For example, a first channel, witha greater transmission power than a second channel after attenuation,may be associated with a lower bit error rate after transmission.

Network management device 210 may determine the bit error rate bymonitoring one or more network devices 230, in some implementations. Forexample, network management device 210 may monitor a set of bitstransmitted by a set of Tx devices 240 and received by a set of Rxdevices 275. In some implementations, the set of bits may be attenuatedby a pass-band filter of a first WSS 320 associated with a first ROADM260 that includes Tx devices 240. Additionally, or alternatively, theset of bits may be attenuated by a pass-band filter of a second WSS 320associated with a second ROADM 260 that includes Rx devices 275.Additionally, or alternatively, the set of bits may be attenuated by oneor more pass-band filters of one or more WSSs 320 associated with one ormore ROADMs 260 associated with routing the set of bits from first ROADM260 to second ROADM 260.

As further shown in FIG. 5, process 500 may include determining that abit error rate for the set of channels does not satisfy a bit error ratethreshold (block 520). For example, network management device 210 maydetermine that the bit error rate for the set of channels does notsatisfy a threshold. In some implementations, network management device210 may determine that the bit error rate does not satisfy a bit errorrate threshold based on the bit error rate for a particular channel ofthe set of channels. In some implementations, network management device210 may determine that the bit error rate does not satisfy a thresholdassociated with a differential bit error rate (e.g., a difference in afirst bit error rate for a first channel of a super-channel comparedwith a second bit error rate for a second channel of the super-channel,or the like).

Network management device 210 may determine the threshold based on oneor more factors, in some implementations. For example, networkmanagement device 210 (e.g., or an operator, thereof) may determine arisk of damage to a component of ROADM 260 as a consequence of alteringa bit error rate, and may set a particular threshold so that acost-benefit of the risk of damage is outweighed by degraded networkperformance associated with the bit error rate.

Additionally, or alternatively, network management device 210 maydetermine that a first network usage is associated with a firstthreshold and a second network usage is associated with a secondthreshold. For example, network management device 210 (e.g., or anoperator, thereof) may determine that a first type of information iscomparatively less error-tolerant than a second type of information, andnetwork management device 210 may select a comparatively lower bit errorrate threshold for when ROADM 260 is configured to route the first typeof information than the bit error rate threshold for when ROADM 260 isconfigured to route the second type of information.

In some implementations, network management device 210 may determine anetwork performance score based on a set of factors (e.g., a bit errorrate factor, a power management factor, a risk of component failurefactor, or the like), and may select a threshold based on maximizing thenetwork performance score for a super-channel, for a particular channel,or the like. Additionally, or alternatively, network management device210 may select a bit error rate threshold based on determining anavailability of one or more other techniques for reducing WSSfilter-based impairment.

As further shown in FIG. 5, process 500 may include adjusting atransmission power for one or more channels of the set of channels(block 530). For example, network management device 210, may performcomparative channel pre-emphasis by adjusting the transmission power forone or more channels of the set of channels based on determining thatthe bit error rate does not satisfy the threshold. Comparative channelpre-emphasis may refer to increasing a transmission power of a firstchannel as compared to a transmission power of a second channel prior toattenuation via the pass-band filter. In this way, a bit error rateand/or a differential bit error rate associated with WSS filter-basedimpairment may be reduced resulting in increased network performance.

In some implementations, network management device 210 may increase thetransmission power for a particular channel, of the set of channels, tolower a bit error rate. For example, when the particular channel isassociated with a higher bit error rate than another channel, networkmanagement device 210 may utilize an amplifier, configure Tx device 240,configure a variable optical attenuator, or the like to increasetransmission power associated with the particular channel. In this way,network management device 210 may lower a bit error rate associate withthe particular channel, thereby decreasing a differential bit error ratebetween the particular channel and the other channel.

In some implementations, network management device 210 may decrease atransmission power for a particular channel, of the set of channels, toraise a bit error rate. For example, when the particular channel isassociated with a lower bit error rate than another channel, networkmanagement device 210 may configure Tx device 240, a variable opticalattenuator, or the like, to decrease transmission power for theparticular channel. In this way, network management device 210 may raisea bit error rate associated with the particular channel, therebydecreasing a differential between the bit error rate of the particularchannel and the other bit error rate of the other channel.

In some implementations, network management device 210 may cause atransmitter to redistribute information that was to be transferred via achannel. For example, network management device 210 may causeinformation associated with a first channel to be transmitted via asecond channel based on altering the transmission power of the firstchannel and/or the second channel.

In some implementations, network management device 210 may perform oneor more other techniques to reduce the impact of WSS filter-basedimpairment, such as using differentiated channel modulation formats(e.g., as described with respect to FIG. 7), multi-channel forward errorcorrection interleaving (e.g., as described with respect to FIGS. 9A and9B), differentiated channel baud rates (e.g., as described with respectto FIG. 11), selective subcarrier adjustment (e.g., as described withrespect to FIG. 13), or the like. For example, when network managementdevice 210 determines that raising a transmission power for a channel toa first power outweighs the risk of component damage and raising thetransmission power for the channel to a second power does not outweighthe risk of component damage, network management device 210 may raisethe transmission to the first power to lower a bit error rate to a firstbit error rate, and network management device 210 may utilizedifferentiated channel baud rates to lower the bit error rate to asecond, lower bit error rate. In this way, network management device 210may combine multiple techniques that reduce the impact of WSSfilter-based impairment to achieve greater network performance than maybe achieved utilizing a single technique.

In some implementations, network management device 210 may utilize afeedback loop to control adjustment of a transmission power of achannel. For example, network management device 210 may monitor opticalnetwork 220 and return to block 510.

Although FIG. 5 shows process 500 as being performed by networkmanagement device 210, comparative channel pre-emphasis may be performedprior to installation of an optical transport network. For example, itmay be determined, based on testing, simulation, or the like, that aparticular bit error rate will be associated with a particular channel,a set of Tx devices 240 may be configured utilizing differentialtransmission powers to perform comparative channel pre-emphasis (withoutinteraction with network management device 210), and a set of Rx devices275 may be configured to receive optical signals from the set of Txdevices 240 (without interaction with network management device 210).

Although FIG. 5 shows example blocks of process 500, in someimplementations, process 500 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 5. Additionally, or alternatively, two or more of theblocks of process 500 may be performed in parallel.

FIGS. 6A and 6B are diagrams of an example implementation 600 relatingto example process 500 shown in FIG. 5. FIGS. 6A and 6B show an exampleof reducing WSS filter-based impairment using comparative channelpre-emphasis.

As shown in FIG. 6A, a transmitter of ROADM 260 may include atransmitter digital signal processor (Tx DSP) 605, one or moredigital-to-analog converters (DACs) 610, a laser 615, one or moremodulators 620, and one or more variable optical attenuators 625. Insome implementations, Tx DSP 605, DACs 610, laser 615, modulators 620,and/or variable optical attenuators 625 may be implemented on one ormore integrated circuits, such as one or more PICs, one or more ASICs,or the like. In some implementations, components of multipletransmitters may be implemented on a single integrated circuit, such asa single PIC, to form a super-channel transmitter.

Tx DSP 605 may include a digital signal processor or a collection ofdigital signal processors. In some implementations, Tx DSP 605 mayreceive a data source (e.g., a signal received via a Tx channel), mayprocess the signal, and may output digital signals having symbols thatrepresent components of the signal (e.g., an in-phase x-polarizationcomponent, a quadrature x-polarization component, an in-phasey-polarization component, and a quadrature y-polarization component).

DAC 610 may include a digital-to-analog converter or a collection ofdigital-to-analog converters. In some implementations, DAC 610 mayreceive respective digital signals from Tx DSP 605, may convert thereceived digital signals to analog signals, and may provide the analogsignals to modulator 620. The analog signals may correspond toelectrical signals (e.g., voltage signals) to drive modulator 620. Insome implementations, a transmitter may include multiple DACs 610, wherea particular DAC 610 may correspond to a particular polarization (e.g.,an x-polarization, a y-polarization) of a signal and/or a particularcomponent of a signal (e.g., an in-phase component, a quadraturecomponent).

Laser 615 may include a semiconductor laser, such as a distributedfeedback (DFB) laser, or some other type of laser. Laser 615 may providean output optical light beam to modulator 620.

Modulator 620 may include a Mach-Zehnder modulator (MZM), such as anested MZM, or another type of modulator. Modulator 620 may receive theoptical light beam from laser 615 and the voltage signals from DAC 610,and may modulate the optical light beam, based on the voltage signals,to generate a multiple subcarrier output signal, which may be providedto a multiplexer.

In some implementations, a transmitter may include multiple modulators620, which may be used to modulate signals of different polarizations.For example, an optical splitter may receive an optical light beam fromlaser 615, and may split the optical light beam into two branches: onefor a first polarization (e.g., an x-polarization) and one for a secondpolarization (e.g., the y-polarization). The splitter may output oneoptical light beam to a first modulator 620, which may be used tomodulate signals of the first polarization, and another optical lightbeam to a second modulator 620, which may be used to modulate signals ofthe second polarization. In some implementations, two DACs 610 may beassociated with each polarization. In these implementations, two DACs610 may supply voltage signals to the first modulator 620 (e.g., for anin-phase component of the x-polarization and a quadrature component ofthe x-polarization), and two DACs 610 may supply voltage signals to thesecond modulator 620 (e.g., for an in-phase component of they-polarization and a quadrature component of the y-polarization). Theoutputs of modulators 620 may be combined back together using combinersand polarization multiplexing. For example, a combiner, such as apower-combiner, an AWG, a WSS, a fixed passive spectral filter, or thelike, (not shown) may combine a set of modulated optical signals andprovide the output signal.

Variable optical attenuator 625 may include one or more devicesassociated with selectively altering a transmission power of an opticalsignal. For example, variable optical attenuator may be configured toreduce a transmission power associated with a channel of asuper-channel. In some implementations, variable optical attenuator 625may be reconfigured to reduce a quantity of attenuation, therebyincreasing a transmission power of the output signal. In someimplementations, variable optical attenuator 625 may receive modulatedoptical signals from modulator 620, attenuate the modulated opticalsignals to produce an output signal, and provide the output signal.

As further shown in FIG. 6A, and by reference number 630, networkmanagement device 210 may receive transmission information regarding abit error rate of a set of channels being provided by the transmitter,and as shown by reference number 635, provide feedback informationassociated with causing variable optical attenuator 625 to attenuate achannel to reduce a transmission power for the channel, therebyperforming comparative channel pre-emphasis. Additionally, oralternatively, network management device 210 may cause variable opticalattenuator 625 to reduce attenuation of the channel to increase a powerfor the channel, thereby performing comparative channel pre-emphasis.Additionally, or alternatively, network management device 210 mayprovide feedback information to one or more other components of thetransmitter, such as Tx DSP 605, DAC 610, laser 615, modulator 620, orthe like to reduce or increase a transmission power associated with achannel, of a set of channels, thereby performing comparative channelpre-emphasis.

The number and arrangement of components shown in FIG. 6A are providedas an example. In practice, a transmitter performing comparative channelpre-emphasis may include additional components, fewer components,different components, or differently arranged components than thoseshown in FIG. 6A. Additionally, or alternatively, a set of componentsshown in FIG. 6A may perform one or more functions described herein asbeing performed by another set of components shown in FIG. 6A.

As shown in FIG. 6B, and by reference number 640, a transmitter maytransmit a set of channels toward a WSS (e.g., a first channel, a secondchannel, a third channel, and a fourth channel). The transmittertransmits each channel utilizing the same power level. The first channeland the fourth channel experience greater attenuation as a result of thepass-band filter than the second channel and the third channel. As shownby reference number 645, the transmission power after attenuation by apass-band filter of the WSS is less for the first and fourth channelcompared with the second and third channel. As shown by reference number650, based on attenuation from the pass-band filter, the first channeland the fourth channel have greater bit error rates than the secondchannel and the third channel. Assume that network management device 210performs comparative channel pre-emphasis. As shown by reference number655, transmission power for the first channel and the fourth channelprior to attenuation by the pass-band filter is increased. As shown byreference number 660, the transmission power for the first channel andthe fourth channel after attenuation by the pass-band filter isincreased based on the pre-attenuation power being increased. As shownby reference number 665, the bit error rate for the first channel andthe fourth channel decreases based on the transmission power afterattenuation increasing. Assume that network management device 210further performs comparative channel pre-emphasis. As shown by referencenumber 670, transmission power pre-attenuation for the first channel andthe fourth channel increases and transmission power for the secondchannel and the third channel decreases. As shown by reference number675, transmission power post-attenuation increases for the first channeland fourth channel and decreases for the second channel and thirdchannel. As shown by reference number 670, the bit error rate for thefirst channel and the fourth channel decreases and the bit error ratefor the second channel and the third channel increases, thereby reducinga differential bit error rate.

As indicated above, FIGS. 6A and 6B are provided merely as an example.Other examples are possible and may differ from what was described withregard to FIGS. 6A and 6B.

FIG. 7 is a flow chart of an example process 700 for reducing WSSfilter-based impairment using differentiated channel modulation formats.In some implementations, one or more process blocks of FIG. 7 may beperformed by network management device 210. In some implementations, oneor more process blocks of FIG. 7 may be performed by another componentor a set of components separate from or including network managementdevice 210, such as network device 230 (e.g., Tx device 240, MUX 250,ROADM 260, DEMUX 270, Rx device 275) or the like.

As shown in FIG. 7, process 700 may include monitoring a set of channelsto determine a bit error rate (block 710). For example, networkmanagement device 210 may monitor the set of channels to determine thebit error rate. In some implementations, the bit error rate maycorrespond to a modulation format. For example, a first channel with afirst modulation format may be associated with a different bit errorrate than a second channel with a second modulation format. In someimplementations, network management device 210 may determine the biterror rate based on receiving information from one or more components ofa transmitter, as discussed herein with respect to FIG. 5. In someimplementations, network management device 210 may monitor the set ofchannels to determine another signal quality factor, such as a signal tonoise ratio, a Q-factor, or the like.

As further shown in FIG. 7, process 700 may include determining that abit error rate for the set of channels does not satisfy a threshold(block 720). For example, network management device 210 may determinethat the bit error rate does not satisfy a bit error rate thresholdand/or a differential bit error rate threshold, as discussed herein withrespect to FIG. 5, and may determine to alter a modulation format basedon determining that the bit error rate does not satisfy the bit errorrate threshold. A particular modulation format may be associated with aparticular bit error rate when attenuated by a pass-band filter and aparticular data transmission rate. For example, quadrature phase shiftkeying (QPSK) may be associated with a greater bit error rate and agreater data transmission rate than binary phase shift keying (BPSK).Similarly, 8-quadrature amplitude modulation (8-QAM) may be associatedwith a greater bit error rate and a greater data transmission rate thanQPSK, and 16-QAM may be associated with a greater bit error rate and agreater data transmission rate than 8-QAM. Additionally, oralternatively, different modulation formats may correspond to differentpotential data transfer distances.

In some implementations, network management device 210 may select thethreshold based on a modulation format criteria. For example, networkmanagement device 210 may determine a particular bit error ratethreshold for adjusting from a first modulation format to a secondmodulation format based on a change to a data transmission rate andpotential transmission distance associated therewith. Similarly, networkmanagement device 210 may determine another bit error rate threshold foradjusting from the first modulation format to a third modulation formatbased on a change to a data transmission rate and potential transmissiondistance associated therewith.

In some implementations, network management device 210 may determine anetwork performance score based on a set of factors (e.g., a bit errorrate factor, a modulation format factor, such as a data transmissionrate factor, a potential transmission distance factor, or the like), andmay select a threshold based on the network performance score for asuper-channel, for a particular channel, or the like. Additionally, oralternatively, network management device 210 may select the thresholdbased on determining an availability of one or more other techniques forreducing WSS filter-based impairment.

As further shown in FIG. 7, process 700 may include adjusting amodulation format for one or more channels of the set of channels (block730). For example, network management device 210 may reduce WS Sfilter-based impairment using differentiated channel modulation formatsbased on determining that the threshold is not satisfied. Differentiatedchannel modulation formats may refer to utilizing different signalmodulation formats for multiple channels. For example, networkmanagement device 210 may cause a first channel to be modulated using afirst modulation format and a second channel to be modulated using asecond modulation format.

In some implementations, network management device 210 may cause aparticular channel to be modulated with a modulation format that resultsin decreased bit error rate. For example, when a particular channel isassociated with a greater bit error rate than another channel (e.g.,caused by attenuation via a pass-band filter associated with WSS 320),network management device 210 may decrease a bit error rate associatedwith the particular channel by altering its modulation format from QPSKto BPSK. In this way, network management device 210 may reduce adifferential bit error rate between the particular channel and the otherchannel.

Additionally, or alternatively, when the particular channel isassociated with a lower bit error rate than another channel, networkmanagement device 210 may increase a bit error rate associated with theparticular channel by altering modulation format from QPSK to BPSK. Inthis way, network management device 210 may reduce a differential biterror rate between the particular channel and the other channel.

Additionally, or alternatively, network management device 210 mayincrease a bit error rate associated with a first channel by alteringits modulation format from QPSK to 8-QAM, and decrease a bit error rateassociated with a second channel by altering its modulation format fromQPSK to BPSK. In some implementations, network management device 210 maycause a transmitter to redistribute information that was to betransferred via a channel. For example, network management device 210may cause information associated with a first channel to be transmittedvia a second channel based on altering the channels.

In some implementations, network management device 210 may perform oneor more other techniques to reduce the impact of WSS filter-basedimpairment, such as using comparative channel pre-emphasis (e.g., asdescribed with respect to FIG. 5), multi-channel forward errorcorrection interleaving (e.g., as described with respect to FIGS. 9A and9B), differentiated channel baud rates (e.g., as described with respectto FIG. 11), selective subcarrier adjustment (e.g., as described withrespect to FIG. 13), or the like. For example, network management device210 may alter a modulation format from 8-QAM to QPSK and utilizecomparative channel pre-emphasis to reduce a bit error rate withoutoverly reducing a data rate and/or a potential transmission distance. Inthis way, network management device 210 may combine multiple techniquesthat reduce the impact of WSS filter-based impairment to achieve greateroptical transport network performance than may be achieved utilizing asingle technique.

In some implementations, network management device 210 may utilize afeedback loop to control adjusting a modulation format. For example,network management device 210 may monitor optical network 220 and returnto block 710.

Although FIG. 7 shows process 700 as being performed by networkmanagement device 210, differentiated channel modulation formats may beconfigured prior to installation of an optical transport network. Forexample, it may be determined, based on testing, simulation, or thelike, that a particular bit error rate will be associated with aparticular channel, a set of transmitters may be configured to utilizedifferentiated channel modulation formats for multiple channels (withoutinteraction with network management device 210), and a set of receiversmay be configured to utilize differentiated channel modulation formatsfor multiple channels (without interaction with network managementdevice 210).

Although FIG. 7 shows example blocks of process 700, in someimplementations, process 700 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 7. Additionally, or alternatively, two or more of theblocks of process 700 may be performed in parallel.

FIGS. 8A and 8B are diagrams of an example implementation 800 relatingto example process 700 shown in FIG. 7. FIGS. 8A and 8B show an exampleof reducing WSS filter-based impairment using differentiated channelmodulation formats.

As shown in FIG. 8A, a set of transmitters of ROADM 260, may include oneor more transmitter digital signal processors (Tx DSPs) 805, one or moredigital-to-analog converters (DACs) 810, one or more lasers 815, and oneor more modulators 820. In some implementations, Tx DSPs 805, DACs 810,lasers 815, and/or modulators 820 may be implemented on one or moreintegrated circuits, such as one or more PICs, one or more ASICs, or thelike. Tx DSP 805 may include a digital signal processor or a collectionof digital signal processors, DAC 810 may include a digital-to-analogconverter or a collection of digital-to-analog converters, laser 815 mayinclude a semiconductor laser or some other type of laser, and modulator620 may include a MZM modulator or another type of modulator, asdescribed herein with respect to FIG. 6A.

In some implementations, modulator 820 may be configured to utilize aset of modulation formats, such as BPSK, QPSK, 8-QAM, 16-QAM, or thelike. In some implementations, network management device 210 may providean indication of a particular modulation format that a particularmodulator 820 is to utilize. Additionally, or alternatively, modulator820 may be configured to utilize a single particular modulation format,and may be installed in ROADM 260 to provide channels utilizing theparticular modulation format based on an expected attenuation of signalsby a pass-band filter.

As further shown by FIG. 8A, and by reference number 825, for an exampleset of transmitters associated with ROADM 260, modulator 820-1 may beassociated with providing transmissions utilizing BPSK modulation. Asshown by reference number 830, modulator 820-2 may be associated withutilizing QPSK modulation. As shown by reference number 835, modulator820-3 may be associated with utilizing QPSK modulation. As shown byreference number 840, modulator 820-4 may be associated with utilizingBPSK modulation. In some implementations, a set of de-modulatorsassociated with a set of receivers (e.g., that may correspond to Rxdevice 275) may be configured to de-modulate channels transmitted by theexample set of transmitters associated with ROADM 260.

The number and arrangement of components shown in FIG. 8A are providedas an example. In practice, a transmitter utilizing differentiatedchannel modulation formats may include additional components, fewercomponents, different components, or differently arranged componentsthan those shown in FIG. 8A. Additionally, or alternatively, a set ofcomponents shown in FIG. 8A may perform one or more functions describedherein as being performed by another set of components shown in FIG. 8A.

As shown in FIG. 8B, and by reference number 845, a set of channels areassociated with a set of wavelengths and a corresponding modulationformat (e.g., a first channel associated with QPSK, a second channelassociated with QPSK, a third channel associated with QPSK, and a fourthchannel associated with QPSK). As shown by reference number 850, thefirst channel and the fourth channel are attenuated more than the secondchannel and the third channel, resulting in a greater bit error rate forthe first channel and the fourth channel compared with the secondchannel and the third channel. As shown by reference number 855, basedon utilizing QPSK for each channel of the set of channels, each channelhas the same data rate. Assume one or more transmitters associated withtransmitting the set of channels are reconfigured and, as shown byreference number 860, the first channel is altered to be associated withBPSK modulation, the second channel is associated with QPSK modulation,the third channel is associated with QPSK modulation, and the fourthchannel is altered to be associated with BPSK modulation. As shown byreference number 865, based on altering modulation formats for the firstchannel and the fourth channel, bit error rates for the first channeland the fourth channel are reduced. As shown by reference number 870,based on altering modulation formats for the first channel and thefourth channel, data rates for the first channel and the fourth channelare reduced.

As indicated above, FIGS. 8A and 8B are provided merely as an example.Other examples are possible and may differ from what was described withregard to FIGS. 8A and 8B.

FIGS. 9A and 9B are flow charts of an example process 900 for reducingWSS filter-based impairment using multi-channel forward error correctionaveraging via an interleaving process. In some implementations, one ormore process blocks of FIGS. 9A and 9B may be performed by networkmanagement device 210. In some implementations, one or more processblocks of FIG. 5 may be performed by another component or a set ofcomponents separate from or including network management device 210,such as network device 230 (e.g., Tx device 240, MUX 250, ROADM 260,DEMUX 270, Rx device 275) or the like.

As shown in FIG. 9A, process 900 may include determining to performforward error correction (FEC) interleaving (block 910). For example,network management device 210 may determine to perform FEC interleaving.FEC may refer to appending error correction information that describespayload information (e.g., information that is to be transmitted via aset of optical signals) to the payload information allowing a receiverto determine the payload information despite bit errors in the payloadinformation. In some implementations, FEC may be associated with amaximum bit error rate threshold. In some implementations, FEC may beassociated another signal quality factor threshold, such as a signal tonoise ratio threshold, a Q-factor threshold, or the like. For example,error correction information may facilitate reconstruction of payloadinformation from a set of optical signals that includes a set of errorswhen the quantity of errors does not exceed a threshold quantity.

In some implementations, network management device 210 may determine toperform FEC interleaving based on a bit error rate and/or a differentialbit error rate, associated with a super-channel, satisfying a threshold.For example, network management device 210 may determine a bit errorrate threshold and may determine that the bit error rate threshold issatisfied, as described herein with respect to FIG. 5. Additionally, oralternatively, network management device 210 may determine to performFEC interleaving based on an average bit error rate for multiplechannels satisfying a FEC threshold. For example, network managementdevice 210 may determine that when bit errors are averaged acrossmultiple channels, FEC may be performed for each of the multiplechannels, some of the multiple channels, or the like.

In some implementations, network management device 210 may determine toperform FEC interleaving based on a network configuration. For example,network management device 210 and/or one or more network devices 230 maybe configured to perform FEC interleaving when a super-channel includingmultiple channels is being transmitted via optical network 220.

As further shown in FIG. 9A, process 900 may include causing FEC data tobe appended to a set of optical signals associated with a set ofchannels (block 920). For example, network management device 210 maycause FEC data to be appended (e.g., by a transmitter) to the set ofoptical signals associated with the set of channels. In someimplementations, the FEC data may include error correction information,such as a set of bits associated with payload information of the set ofoptical signals. For example, network management device 210 may causeredundant bits associated with the payload information (e.g., a set ofredundant bits that permit a receiver to determine the payloadinformation when an error is located within another set of bits of thepayload information and/or the set of redundant bits) to be appended toa portion of an optical signal. Additionally, or alternatively, FEC datamay include information associated with performing FEC, such as aninformation identifying a bit redundancy, identifying an interleavingalgorithm, or the like.

As further shown in FIG. 9A, process 900 may include causing a set ofportions of the set of optical signals to be interleaved (block 930).For example, network management device 210 may cause a transmitter ofROADM 260 and/or another similar device to interleave the set ofportions of the set of optical signals. In some implementations, networkmanagement device 210 may utilize a particular interleaving algorithmwhen causing the transmitter of ROADM 260 to interleave the set ofportions of the set of optical signals. For example, network managementdevice 210 may provide a particular rearrangement algorithm to a FECinterleaver component of the transmitter and may provide the particularrearrangement algorithm to a FEC de-interleaver component of a receiver(e.g., a receiver associated with another ROADM 260).

In some implementations, network management device 210 may cause thetransmitter of ROADM 260 to interleave portions of a particular channelwithin the particular channel. For example, the transmitter mayrearrange bits of a portion of the particular channel according to aninterleaving algorithm. In this way, bit errors, which may occur morecommonly in proximity to one another, are averaged among locations ofthe particular channel at the receiver when the bits are de-interleavedinstead of being concentrated at a particular location of the particularchannel, thereby facilitating FEC.

Additionally, or alternatively, network management device 210 may causethe transmitter of ROADM 260 to interleave portions of multiple channelsbetween the multiple channels. For example, the transmitter may divide aportion of information that is to be transmitted via a first channelinto a first portion and a second portion and may cause the firstportion to be provided via the first channel and the second portion tobe provided via the second channel. Similarly, the transmitter maydivide a portion of information that is to be transmitted via the secondchannel into a third portion and a fourth portion and may cause thethird portion to be transmitted via the first channel and the fourthportion to be transmitted via the second channel. In this way, atransmitter may avoid concentration of bit errors on information beingtransmitted via any particular channel by interleaving a set of channelsand then de-interleaving the set of channels to spread bit errors acrossthe set of channels, thereby facilitating FEC.

As further shown in FIG. 9A, process 900 may include causing the set ofoptical signals to be transmitted (block 940). For example, networkmanagement device 210 may cause the set of optical signals to betransmitted (e.g., by a transmitter). In some implementations, networkmanagement device 210 may cause a transmitter of ROADM 260 to providethe set of optical signals to a passive power splitter, may cause theset of optical signals to be power split and provided to a set of WSSswith a set of pass-band filters, and may cause the set of opticalsignals to be routed via a set of other ROADMs to a receiver. In someimplementations, the set of optical signals may incur a set of biterrors associated with signal noise, attenuation by one or morepass-band filters associated with one or more WSSs, or the like duringtransmission.

As shown in FIG. 9B, process 900 may include causing a set ofinterleaved optical signals transmitted via a set of optical channels tobe received (block 950). For example, network management device 210 maycause a receiver device associated with ROADM 260 or another type ofdevice to receive the set optical signals that have been interleaved. Insome implementations, network management device 210 may cause the set ofoptical signals to be received by a WSS of a ROADM, passed through apass-band filter, and routed to a receiver device. In someimplementations, network management device 210 may determine that theset of optical signals have been interleaved based on receivinginformation from a transmitter of another ROADM 260, from anothernetwork management device 210, or the like.

As further shown in FIG. 9B, process 900 may include causing a set ofportions of the set of channels to be de-interleaved (block 960). Forexample, network management device 210 may cause a FEC de-interleavercomponent of a receiver of ROADM 260 to de-interleave the set ofportions of the set of channels. In some implementations, networkmanagement device 210 may provide information identifying ade-interleaving algorithm. For example, network management device 210may provide information associated with re-arranging a set of bitswithin the set of optical signals, a set of portions between the opticalsignals, or the like.

As further shown in FIG. 9B, process 900 may include causing FEC dataappended to the set of optical signals to be utilized to perform FEC(block 970). For example, network management device 210 may cause areceiver of ROADM 260 to utilize the FEC data that was appended to theset of optical signals to perform FEC on the de-interleaved set ofchannels. In some implementations, network management device 210 mayutilize one or more other techniques to reduce WSS filter-basedimpairment in combination with multi-channel FEC interleaving. In someimplementations, the receiver may perform FEC based on a FEC algorithmto recover payload information associated with the set of channels. Inthis way, multiple channels may be utilized with FEC to improve networkperformance by reducing lost payload information.

Although FIGS. 9A and 9B shows process 900 as being performed based onmonitoring optical network 220, multi-channel FEC interleaving may beconfigured prior to installation of an optical transport network. Forexample, it may be determined, based on testing, simulation, or thelike, that a particular bit error rate will be associated with aparticular channel, and a set of transmitters may be configured toperform multi-channel FEC interleaving (without interaction with networkmanagement device 210), and a set of receivers may be configured toperform multi-channel FEC interleaving (without interaction with networkmanagement device 210).

Although FIGS. 9A and 9B shows example blocks of process 900, in someimplementations, process 900 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIGS. 9A and 9B. Additionally, or alternatively, two or moreof the blocks of process 900 may be performed in parallel.

FIGS. 10A-10D are diagrams of an example implementation 1000 relating toexample process 900 shown in FIGS. 9A and 9B. FIGS. 10A-10D show anexample of reducing WSS filter-based impairment using multi-channelforward error correction averaging via an interleaving process.

As shown in FIG. 10A, optical network 220 may include a set of Txdevices 240-1 through 240-M (M≧1), which may include a set ofcorresponding FEC encoders 1005-1 through 1005-M (hereinafter referredto individually as “FEC encoder 1005,” and collectively as “FEC encoders1005”); a FEC interleaver 1010; a FEC de-interleaver 1015; and a set ofRx devices 275-1 through 275-M, which may include a set of correspondingFEC decoders 1020-1 through 1020-M (hereinafter referred to individuallyas “FEC decoder 1020,” and collectively as “FEC decoders 1020”).

Tx device 240 may include a transmitter, as described herein withrespect to FIG. 2B. In some implementations, Tx device 240 may include aset of components, such as a Tx DSP, a DAC, a laser, a modulator, or thelike, as described herein with respect to FIG. 6A. In someimplementations, one or more Tx devices 240 may be associated withreceiving input data and generating a set of optical signals associatedwith transmitting the input data via multiple channels. In someimplementations, the multiple channels may be associated with one ormore super-channels. In some implementations, Tx device 240 may includeand/or be associated with FEC encoder 1005, FEC interleaver 1010, or thelike.

FEC encoder 1005 may include a component capable of receiving,generating, processing, and/or providing information associated withperforming FEC. In some implementations, FEC encoder 1005 may generateFEC data that includes a set of error correction bits corresponding to aset of payload bits of an optical signal associated with facilitatingreconstruction of the optical signal after transmission of the opticalsignal. In some implementations, FEC encoder 1005 may utilize aparticular algorithm for generating the FEC data. In someimplementations, FEC encoder 1005 may provide information associatedwith determining the payload information based on the FEC data.

FEC interleaver 1010 may include a component capable of receiving,generating, processing, and/or providing information associated with anoptical signal. In some implementations, FEC interleaver 1010 mayrearrange bits of the optical signal within a channel of asuper-channel. Additionally, or alternatively, FEC interleaver 1010 mayrearrange portions of the optical signal between multiple channels of asuper-channel. In some implementations, FEC interleaver 1010 mayinterleave the optical signal based on an interleaving algorithm.Additionally, or alternatively, FEC interleaver 1010 may provideinformation (e.g., to FEC de-interleaver 1015) associated withde-interleaving the optical signal. In some implementations, FECinterleaver 1010 may not alter FEC data associated with a channel whenperforming FEC interleaving. For example, when first FEC data isgenerated regarding a first channel and second FEC data is generatedregarding a second channel, the first FEC data and the second FEC datamay remain unchanged when interleaving is performed on the first channeland the second channel. In this case, the first FEC data and the secondFEC data may not be usable to recover bits of the first channel and thesecond channel until the first channel and the second channel arede-interleaved.

FEC de-interleaver 1015 may include a component capable of receiving,generating, processing, and/or providing information associated with anoptical signal. In some implementations, FEC de-interleaver 1015 mayde-interleave bits of a set of optical signals within a channel,portions of a set of optical signals between multiple channels, or thelike. In some implementations, FEC de-interleaver 1015 may performde-interleaving based on an algorithm (e.g., a configured algorithm, aprovided algorithm, or the like).

Rx device 275 may include a receiver, as described herein with respectto FIG. 2B. In some implementations, Rx device 275 may include a set ofcomponents, such a local oscillator, a hybrid mixer, a detector, ananalog-to-digital converter, a receiver digital signal processor (RxDSP), or the like. In some implementations, one or more Rx devices 275may be associated with receiving input data and generating a set ofoptical signals associated with transmitting the input data via multiplechannels. In some implementations, the multiple channels may beassociated with one or more super-channels. In some implementations, Rxdevice 275 may include and/or be associated with FEC decoder 1020, FECde-interleaver 1015, or the like.

FEC decoder 1020 may include a component capable of receiving,generating, processing, and/or providing information associated withperforming FEC. In some implementations, FEC decoder 1020 may determineFEC data that includes a set of error correction bits corresponding to aset of payload bits of an optical signal associated with facilitatingreconstruction of the optical signal after transmission of the opticalsignal. In some implementations, FEC decoder 1020 may utilize aparticular algorithm for processing the FEC data to perform FEC. In someimplementations, FEC decoder 1020 may provide payload informationassociated with a set of optical signals based on performing FEC.

The number and arrangement of components shown in FIG. 10A are providedas an example. In practice, a transmitter performing multi-channel FECinterleaving may include additional components, fewer components,different components, or differently arranged components than thoseshown in FIG. 10A. Additionally, or alternatively, a set of componentsshown in FIG. 10A may perform one or more functions described herein asbeing performed by another set of components shown in FIG. 10A.

As shown in FIG. 10B, and by reference number 1025, a set of fourchannels include payload information with a set of redundant bits (e.g.,“AAAA, BBBB, . . . ,” “EEEE, FFFF, . . . ,” etc.). Assume that the finalblock of each channel represents FEC data appended to each channel(e.g., “DDDD,” “HHHH,” “NNNN,” and “UUUU”). Assume that the firstchannel and the fourth channel are edge channels and the second channeland the third channel are interior channels. As shown by referencenumber 1030, the set of four channels are transmitted withoutinterleaving resulting in a set of bit errors. Assume that FEC may beperformed to recover payload data if more than two bits of a four bitblock are transmitted without error and that bit errors occur morecommonly for data transmitted via the edge channels compared with theinterior channels as a result of impairment by one or more pass-bandfilters associated with one or more WSSs (e.g., the edge channels areattenuated by the one or more pass-band filters more than the interiorchannels). As shown by reference number 1035, without performinginterleaving, the edge channels incur 50% bit error rates while theinterior channels incur 0% bit error rates as a result of impairment bythe one or more pass-band filters. Based on the quantity of bits beingsuccessfully transmitted not exceeding two bits per block, only the 8blocks of the interior channels, out of 16 blocks that are transmittedvia the set of four channels, are recovered.

As shown in FIG. 10C, and by reference number 1040, assume that FECinterleaver 1010 performs FEC interleaving within each of the multiplechannels and between the multiple channels. Bits of a particular channelare interleaved with other bits of the particular channel (e.g., “AAAA,BBBB, . . . ” interleaves to “ABCD, ABCD, . . . ,” “EEEE, FFFF, . . . ”interleaves to “EFGH, EFGH, . . . ,” etc.). Portions of each channel areinterleaved with other portions of each channel (e.g., “ABCD, ABCD, . .. ” interleaves to “ABCD, EFGH, . . . ,” “KLMN, KLMN, . . . ”interleaves to “KLMN, RSTU, . . . ,” etc.). As shown by reference number1045, the set of four channels are transmitted with interleaving of bitswithin each channel and with interleaving of portions of each channelamong the multiple channels and incurring a set of bit errors. As shownby reference number 1050, prior to de-interleaving, the edge channelsincur 50% bit error rates while the interior channels incur 0% bit errorrates as a result of impairment by the pass-band filter.

As shown in FIG. 10D, and by reference number 1055, FEC de-interleaver1015 performs de-interleaving of the set of four interleaved channels(e.g., “A.D,” “E.G.,” etc. de-interleaves to “A.AA,” “.BBB,” etc.). Whende-interleaved, each channel, of the set of four de-interleavedchannels, incurs a 25% bit error rate. As shown by reference number1060, FEC decoder 1020 performs FEC decoding on the set of fourde-interleaved channels. As a result of the bit error rate beingaveraged across the set of four de-interleaved channels, 16 blocks, outof 16 transmitted blocks, are recovered based on performing FECdecoding. In this way, performing FEC interleaving between multiplechannels results in greater information recovery of transmittedinformation than without FEC interleaving, thereby improving the fieldof optical network management through reduced information loss duringoptical transmissions.

In this way, multiple channels may be utilized to spread bit errorsconcentrated on edge channels among information of the multiple channels(e.g., that include the edge channels and one or more interior channels)to avoid a concentration of bit errors that may render FEC ineffectivefor recovering information of the edge channels.

As indicated above, FIGS. 10A-10D are provided merely as an example.Other examples are possible and may differ from what was described withregard to FIGS. 10A-10D.

FIG. 11 is a flow chart of an example process 1100 for reducing WSSfilter-based impairment using differentiated channel baud rates. In someimplementations, one or more process blocks of FIG. 11 may be performedby network management device 210. In some implementations, one or moreprocess blocks of FIG. 11 may be performed by another component or a setof components separate from or including network management device 210,such as network device 230 (e.g., Tx device 240, MUX 250, ROADM 260,DEMUX 270, Rx device 275) or the like.

As shown in FIG. 11, process 1100 may include monitoring a set ofchannels to determine a bit error rate (block 1110). For example,network management device 210 may monitor the set of channels todetermine the bit error rate. In some implementations, networkmanagement device 210 may determine the bit error rate based onreceiving information from one or more components of a transmitter, asdiscussed herein with respect to FIG. 5. In some implementations,network management device 210 may monitor the set of channels todetermine another signal quality factor, such as a signal to noiseratio, a Q-factor, or the like.

As further shown in FIG. 11, process 1100 may include determining that abit error rate for the set of channels does not satisfy a threshold(block 1120). For example, network management device 210 may determinethat the bit error rate and/or a differential bit error rate associatedwith the bit error rate does not satisfy a particular threshold, asdiscussed herein with respect to FIG. 5. In some implementations, aparticular baud rate may be associated with a particular bit error rate,when attenuated by a pass-band filter, and a particular datatransmission rate. For example, for a first channel centered at aparticular wavelength and with a first baud rate and a second channelcentered at the particular wavelength and with a second baud rate, thefirst channel may be associated with a greater bit error rate than thesecond channel when the first baud rate is greater than the second baudrate, as discussed herein with respect to FIG. 12A.

In some implementations, network management device 210 may determine thethreshold based on one or more network criteria. For example, networkmanagement device 210 may determine that a particular network usageshould be associated with a particular data transfer rate and aparticular bit error rate, and may select a threshold that balancesreducing the particular bit error rate against reducing the particulardata transfer rate. Additionally, or alternatively, network managementdevice 210 may determine a set of thresholds. For example, networkmanagement device 210 may determine a first bit error rate threshold fora first network usage is associated with a first data transfer rate anda second bit error rate threshold for a second network usage isassociated with a second data transfer rate.

In some implementations, network management device 210 may determine anetwork performance score based on a set of factors (e.g., a bit errorrate factor, a data transfer rate factor, or the like), and may select athreshold based on the network performance score for a super-channel,for a particular channel, or the like. Additionally, or alternatively,network management device 210 may select the threshold based ondetermining an availability of one or more other techniques for reducingWSS filter-based impairment.

As further shown in FIG. 11, process 1100 may include adjusting a baudrate for one or more channels of the set of channels (block 1130). Forexample, network management device 210 may reduce WSS filter-basedimpairment using differentiated channel baud rates. Differentiatedchannel baud rates may refer to utilizing different baud rates formultiple channels. For example, network management device 210 may causea first channel to be transmitted at a first baud rate and a secondchannel to be transmitted at a second baud rate.

In some implementations, network management device 210 may cause aparticular channel to be transmitted at a particular baud rate thatresults in decreased bit error rate. For example, when a particularchannel is associated with a greater bit error rate than another channel(e.g., caused by attenuation via a pass-band filter associated with WSS320), network management device 210 may decrease a bit error rateassociated with the particular channel by altering a baud rate from afirst, comparatively higher baud rate to a second, comparatively lowerbaud rate. In this way, network management device 210 may reduce adifferential bit error rate between the particular channel and the otherchannel.

In some implementations, network management device 210 may cause aparticular channel to be transmitted at a particular baud rate thatresults in increased bit error rate. For example, when a particularchannel is associated with a lesser bit error rate than another channel(e.g., caused by attenuation via a pass-band filter associated with WSS320), network management device 210 may increase a bit error rateassociated with the particular channel by altering a baud rate from afirst, comparatively lower baud rate to a second, comparatively higherbaud rate. In this way, network management device 210 may reduce adifferential bit error rate between the particular channel and the otherchannel.

Additionally, or alternatively, when a particular channel is associatedwith a lower bit error rate than another channel, network managementdevice 210 may increase a bit error rate associated with the particularchannel by increasing the baud rate and may decrease a bit error rateassociated with the other channel by lowering the baud rate, therebydecreasing a differential bit error rate between the particular channeland the other channel.

In some implementations, network management device 210 may cause atransmitter to redistribute information that was to be transferred via achannel. For example, network management device 210 may causeinformation associated with a first channel to be transmitted via asecond channel based on altering a baud rate associated with the firstchannel and/or the second channel.

In some implementations, network management device 210 may perform oneor more other techniques to reduce the impact of WSS filter-basedimpairment, such as using comparative channel pre-emphasis (e.g., asdescribed herein with respect to FIG. 5), differentiated channelmodulation formats (e.g., as described herein with respect to FIG. 7),multi-channel forward error correction interleaving (e.g., as describedherein with respect to FIGS. 9A and 9B), selective subcarrier adjustment(e.g., as described herein with respect to FIG. 13), or the like. Forexample, network management device 210 may alter a baud rate from afirst baud rate to a second baud rate and utilize multi-channel forwarderror correction interleaving to achieve greater bit error ratereduction than reducing the baud rate alone while mitigating thereduction in data rate associated with reducing the baud rate. In thisway, network management device 210 may combine multiple techniques thatreduce the impact of WSS filter-based impairment to achieve greaternetwork performance than may be achieved utilizing a single technique.

In some implementations, network management device 210 may utilize afeedback loop to control a set of baud rates. For example, networkmanagement device 210 may monitor optical network 220 and return toblock 1110.

Although FIG. 11 shows process 1100 as being performed by networkmanagement device 210, differentiated channel baud rates may beconfigured prior to installation of an optical transport network. Forexample, it may be determined, based on testing, simulation, or thelike, that a particular bit error rate will be associated with aparticular channel, a set of transmitters may be configured to utilizedifferentiated channel baud rates for multiple channels (withoutinteraction with network management device 210), and a set of receiversmay be configured to utilize differentiated channel baud rates formultiple channels (without interaction with network management device210).

Although FIG. 11 shows example blocks of process 1100, in someimplementations, process 1100 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 11. Additionally, or alternatively, two or more of theblocks of process 1100 may be performed in parallel.

FIGS. 12A and 12B are diagrams of an example implementation 1200relating to example process 1100 shown in FIG. 11. FIGS. 12A and 12Bshow an example of reducing WSS filter-based impairment usingdifferentiated channel baud rates.

As shown in FIG. 12A, a set of transmitters of ROADM 260 may include oneor more transmitter digital signal processors (Tx DSP) 1205, one or moredigital-to-analog converters (DACs) 1210, one or more lasers 1215, andone or more modulators 1220. In some implementations, Tx DSPs 1205, DACs1210, lasers 1215, and/or modulators 1220 may be implemented on one ormore integrated circuits, such as one or more PICs, one or more ASICs,or the like. Tx DSP 1205 may include a digital signal processor or acollection of digital signal processors, DAC 1210 may include adigital-to-analog converter or a collection of digital-to-analogconverters, laser 1215 may include a semiconductor laser or some othertype of laser, and modulator 1220 may include a MZM modulator or anothertype of modulator, as described herein with respect to FIG. 6A.

In some implementations, a particular transmitter may be configured toprovide information at a particular baud rate. For example, theparticular transmitter may include a clock device configured tofacilitate baud rate synchronization at the particular baud rate.Additionally, or alternatively, the particular transmitter may beconfigured to provide information at a set of baud rates. For example,the particular transmitter may include a dynamically reconfigurableclock device that may facilitate baud rate synchronization at multiplebaud rates.

As further shown in FIG. 12A, and by reference number 1225, networkmanagement device 210 may control baud rates for the set oftransmitters. As shown by reference number 1230, based on receivinginformation from network management device 210 indicating a particularbaud rate, a first transmitter may provide information utilizing a firstbaud rate and, as shown by reference number 1235, an nth transmitter mayprovide information utilizing an nth baud rate.

As shown in FIG. 12B, and by reference number 1240, a pass-band (e.g.,associated with a pass-band filter) describes attenuation of a set ofchannels (e.g., a first channel, a second channel, a third channel, anda fourth channel) associated with a set of wavelengths by a pass-bandfilter. Although each channel includes the same size width wavelengthrange, the first channel and the fourth channel include areas ofrespective wavelength ranges outside the wavelength range associatedwith the pass-band filter. As shown by reference number 1245, the set ofchannels are associated with the same baud rate, and as shown byreference number 1250, the set of channels are associated with the samedata rate. As shown by reference number 1255, based on the wavelengthranges of the first channel and the fourth channel being outside thewavelength range associated with the pass-band filter, the first channeland the fourth channel are associated with higher bit error rates thanthe second channel and the third channel. Assume that one or moretransmitters associated with transmitting a set of optical signals viathe set of channels are reconfigured to utilize differentiated baudrates. As shown by reference number 1260, based on reducing a baud ratefor the first channel and the fourth channel, the first channel and thefourth channel are associated with narrower respective wavelength rangesthat are not outside the wavelength range associated with the pass-bandfilter. As shown by reference number 1265, the baud rate for the firstchannel and the fourth channel has been reduced to produce the alteredwavelength ranges. As shown by reference number 1270, based on reducingthe baud rate for the first channel and the fourth channel, the datarate for the first channel and the fourth channel is reduced. As shownby reference number 1275, based on reducing the baud rate for the firstchannel and the fourth channel, the bit error rate for the first channeland the fourth channel is reduced.

As indicated above, FIGS. 12A and 12B are provided merely as an example.Other examples are possible and may differ from what was described withregard to FIGS. 12A and 12B.

FIG. 13 is a flow chart of an example process 1300 for reducing WSSfilter-based impairment using selective subcarrier adjustment. In someimplementations, one or more process blocks of FIG. 13 may be performedby network management device 210. In some implementations, one or moreprocess blocks of FIG. 13 may be performed by another component or a setof components separate from or including network management device 210,such as network device 230 (e.g., Tx device 240, MUX 250, ROADM 260,DEMUX 270, Rx device 275) or the like.

As shown in FIG. 13, process 1300 may include monitoring a set ofchannels to determine a bit error rate (block 1310). For example,network management device 210 may monitor the set of channels todetermine the bit error rate. In some implementations, networkmanagement device 210 may determine the bit error rate based onreceiving information from one or more components of a transmitter, asdiscussed herein with respect to FIG. 5. In some implementations,network management device 210 may monitor the set of channels todetermine another signal quality factor, such as a signal to noiseratio, a Q-factor, or the like.

As further shown in FIG. 13, process 1300 may include determining that abit error rate for the set of channels does not satisfy a threshold(block 1320). For example, network management device 210 may determinethat the bit error rate and/or a differential bit error rate does notsatisfy a particular threshold, as discussed herein with respect to FIG.5.

In some implementations, network management device 210 may determine thethreshold based on one or more network criteria. For example, networkmanagement device 210 may determine that a particular network usageshould be associated with a particular data transfer rate and aparticular bit error rate, and may select a threshold that balancesreducing the particular bit error rate against reducing the datatransfer rate by selectively adjusting one or more subcarriers. In someimplementations, network management device 210 may determine multiplethresholds. For example, network management device 210 may determine afirst threshold associated with selectively adjusting a singlesubcarrier and a second threshold associated with selectively adjustingmultiple subcarriers. In some implementations, network management device210 may determine a predicted bit error rate reduction associated withselectively adjusting a particular subcarrier and may select a thresholdbased on the predicted bit error rate reduction.

In some implementations, network management device 210 may determine anetwork performance score based on a set of factors (e.g., a bit errorrate factor, a data transfer rate factor, a predicted bit error ratereduction associated with adjusting a particular subcarrier, or thelike), and may select a threshold based on the network performance scorefor a super-channel, for a particular channel, or the like.Additionally, or alternatively, network management device 210 may selecta threshold based on determining an availability of one or more othertechniques for reducing WSS filter-based impairment.

As further shown in FIG. 13, process 1300 may include adjustingsubcarrier usage for a subcarrier associated with a channel of the setof channels (block 1330). For example, network management device 210 mayreduce WSS filter-based impairment by adjusting a subcarrier usage forthe subcarrier associated the channel of the set of channels. In someimplementations, network management device 210 may select the subcarrierfor which subcarrier usage is adjusted based on a set of factors, suchas a projected bit error rate reduction/increase associated withadjusting the subcarrier usage, information regarding data beingtransferred via the subcarrier, or the like. In some implementations,network management device 210 may cause another device, such as adigital signal processor, or the like to adjust the subcarrier usage.

In some implementations, network management device 210 may cause aparticular channel to be transmitted without a particular subcarrier byblanking the subcarrier. For example, when a particular channel isassociated with a greater bit error rate than another channel (e.g.,caused by attenuation via a pass-band filter associated with WSS 320),network management device 210 may decrease a bit error rate associatedwith the particular channel by blanking a particular subcarrier of thechannel that is associated with a threshold bit error rate. In this way,network management device 210 may reduce a differential bit error ratebetween the particular channel and the other channel.

In some implementations, network management device 210 may alter thesubcarrier. For example, network management device 210 may alter a setof bandwidths associated with the subcarrier, may reduce informationbeing transmitted by the subcarrier, change information beingtransferred by the subcarrier, or the like to reduce a bit error rateassociated with the subcarrier.

In some implementations, network management device 210 may cause atransmitter to redistribute information that was to be transferred viathe subcarrier to one or more other subcarriers. In this way, networkmanagement device 210 may reduce a differential bit error rate betweenthe particular channel and the other channel.

In some implementations, network management device 210 may perform oneor more other techniques to reduce the impact of WSS filter-basedimpairment, such as using comparative channel pre-emphasis (e.g., asdescribed herein with respect to FIG. 5), differentiated channelmodulation formats (e.g., as described herein with respect to FIG. 7),multi-channel forward error correction interleaving (e.g., as describedherein with respect to FIGS. 9A and 9B), differentiated channel baudrates (e.g., as described herein with respect to FIG. 11), or the like.For example, when network management device 210 may alter a omitinformation from a particular subcarrier and utilize multi-channelforward error correction interleaving to achieve greater bit ratereduction than omitting the particular subcarrier alone while mitigatingthe reduction in data rate associated with omitting multiplesubcarriers. In this way, network management device 210 may combinemultiple techniques that reduce the impact of WSS filter-basedimpairment to achieve greater optical transport network performance thanmay be achieved utilizing a single technique.

In some implementations, network management device 210 may utilize afeedback loop to control adjusting a subcarrier usage. For example,network management device 210 may monitor optical network 220 and returnto block 1310.

Although FIG. 13 shows process 1300 as being performed by networkmanagement device 210, selective subcarrier adjustment may be configuredprior to installation of an optical transport network. For example, itmay be determined, based on testing, simulation, or the like, that aparticular bit error rate will be associated with a particularsubcarrier of a particular channel, a set of transmitters may beconfigured to adjust the particular subcarrier to reduce the bit errorrate for the particular channel (without interaction with networkmanagement device 210), and a set of receivers may be configured toreceive based on an adjustment to the particular subcarrier (withoutinteraction with network management device 210).

Although FIG. 13 shows example blocks of process 1300, in someimplementations, process 1300 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 13. Additionally, or alternatively, two or more of theblocks of process 1300 may be performed in parallel.

FIGS. 14A and 14B are diagrams of an example implementation 1400relating to example process 1300 shown in FIG. 13. FIGS. 14A and 14Bshow an example of reducing WSS filter-based impairment using selectivesubcarrier blanking.

As shown in FIG. 14A, a set of transmitters of ROADM 260, may includeone or more transmitter digital signal processors (Tx DSPs) 1405, one ormore digital-to-analog converters (DACs) 1410, one or more lasers 1415,and one or more modulators 1420. In some implementations, Tx DSPs 1405,DACs 1410, lasers 1415, and/or modulators 1420 may be implemented on oneor more integrated circuits, such as one or more PICs, one or moreASICs, or the like. Tx DSP 1405 may include a digital signal processoror a collection of digital signal processors, DAC 1410 may include adigital-to-analog converter or a collection of digital-to-analogconverters, laser 1415 may include a semiconductor laser or some othertype of laser, and modulator 1420 may include a MZM modulator or anothertype of modulator, as described herein with respect to FIG. 6A.

As further shown in FIG. 14A, and by reference number 1425, networkmanagement device 210 controls subcarrier usage for the set oftransmitters. As shown by reference number 1430, a first transmitter mayprovide a first transmission utilizing a first subcarrier usage (e.g.,that includes a first channel with a first set of subcarriers, a secondchannel with a second set of subcarriers, etc.). As shown by referencenumber 1435, an nth transmitter may provide another transmissionutilizing an nth subcarrier usage (e.g., that includes an ath channelwith an ath set of subcarriers, a bth channel with a bth set ofsubcarriers, etc.).

As shown in FIG. 14B, and by reference number 1440, a first channel of asuper-channel may include a set of subcarriers (e.g., subcarrier A,subcarrier B, subcarrier C, subcarrier D, etc.). As shown by referencenumber 1445, a portion of a set of wavelengths associated withsubcarrier A is outside a wavelength range of a pass-band filterdescribed by a pass-band and undergoes attenuation when transmittedthrough the pass-band filter. As shown by reference number 1450, a setof bit error rates for the set of subcarriers indicates that subcarrierA has a higher bit error rate than other subcarriers, of the set ofsubcarriers, and a higher bit error rate than the average bit error rateof the first channel. As shown by reference number 1455, each subcarrieris associated with the same data rate, and collectively a particularcumulative data rate associated with the first channel. As shown byreference number 1460, network management device 210 (not shown) mayindicate that a transmitter associated with transmitting the firstchannel is to discontinue use of an edge subcarrier (e.g., subcarrierA). As shown by reference number 1460, usage of subcarrier A isdiscontinued. As shown by reference number 1465, subcarrier A no longercontributes bit errors to a bit error rate associated with the firstchannel and the average bit error rate associated with the first channeldecreases accordingly. As shown by reference number 1470, subcarrier Ano longer transfers data for the first channel and the cumulative datarate for the first channel decreases accordingly.

As indicated above, FIGS. 14A and 14B are provided merely as an example.Other examples are possible and may differ from what was described withregard to FIGS. 14A and 14B.

FIG. 15 is a diagram of example components of a device 1500. Device 1500may correspond to network management device 210, network device 230,and/or another device described herein. In some implementations, networkmanagement device 210, network device 230, and/or another devicedescribed herein may include one or more devices 1500 and/or one or morecomponents of device 1500. As shown in FIG. 15, device 1500 may includea bus 1510, a processor 1520, a memory 1530, a storage component 1540,an input component 1550, an output component 1560, and a communicationinterface 1570.

Bus 1510 may include a component that permits communication among thecomponents of device 1500. Processor 1520 is implemented in hardware,firmware, or a combination of hardware and software. Processor 1520 mayinclude a processor (e.g., a central processing unit (CPU), a graphicsprocessing unit (GPU), an accelerated processing unit (APU), etc.), amicroprocessor, and/or any processing component (e.g., afield-programmable gate array (FPGA), an application-specific integratedcircuit (ASIC), etc.) that interprets and/or executes instructions.Memory 730 may include a random access memory (RAM), a read only memory(ROM), and/or another type of dynamic or static storage device (e.g., aflash memory, a magnetic memory, an optical memory, etc.) that storesinformation and/or instructions for use by processor 1520.

Storage component 1540 may store information and/or software related tothe operation and use of device 1500. For example, storage component1540 may include a hard disk (e.g., a magnetic disk, an optical disk, amagneto-optic disk, a solid state disk, etc.), a compact disc (CD), adigital versatile disc (DVD), a floppy disk, a cartridge, a magnetictape, and/or another type of computer-readable medium, along with acorresponding drive.

Input component 1550 may include a component that permits device 1500 toreceive information, such as via user input (e.g., a touch screendisplay, a keyboard, a keypad, a mouse, a button, a switch, amicrophone, etc.). Additionally, or alternatively, input component 1550may include a sensor for sensing information (e.g., a global positioningsystem (GPS) component, an accelerometer, a gyroscope, an actuator,etc.). Output component 1560 may include a component that providesoutput information from device 1500 (e.g., a display, a speaker, one ormore light-emitting diodes (LEDs), etc.).

Communication interface 1570 may include a transceiver-like component(e.g., a transceiver, a separate receiver and transmitter, etc.) thatenables device 1500 to communicate with other devices, such as via awired connection, a wireless connection, or a combination of wired andwireless connections. Communication interface 1570 may permit device1500 to receive information from another device and/or provideinformation to another device. For example, communication interface 1570may include an Ethernet interface, an optical interface, a coaxialinterface, an infrared interface, a radio frequency (RF) interface, auniversal serial bus (USB) interface, a Wi-Fi interface, a cellularnetwork interface, or the like.

Device 1500 may perform one or more processes described herein. Device1500 may perform these processes in response to processor 1520 executingsoftware instructions stored by a computer-readable medium, such asmemory 1530 and/or storage component 1540. A computer-readable medium isdefined herein as a non-transitory memory device. A memory deviceincludes memory space within a single physical storage device or memoryspace spread across multiple physical storage devices.

Software instructions may be read into memory 1530 and/or storagecomponent 1540 from another computer-readable medium or from anotherdevice via communication interface 770. When executed, softwareinstructions stored in memory 1530 and/or storage component 1540 maycause processor 1520 to perform one or more processes described herein.Additionally, or alternatively, hardwired circuitry may be used in placeof or in combination with software instructions to perform one or moreprocesses described herein. Thus, implementations described herein arenot limited to any specific combination of hardware circuitry andsoftware.

The number and arrangement of components shown in FIG. 15 are providedas an example. In practice, device 1500 may include additionalcomponents, fewer components, different components, or differentlyarranged components than those shown in FIG. 15. Additionally, oralternatively, a set of components (e.g., one or more components) ofdevice 1500 may perform one or more functions described as beingperformed by another set of components of device 1500.

In this way, a set of network devices may provide CDC broadcastmultiplexing and a set of techniques may reduce WSS filter-basedimpairment associated with the set of network devices and/or another setof network devices.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the implementations to theprecise form disclosed. Modifications and variations are possible inlight of the above disclosure or may be acquired from practice of theimplementations.

As used herein, the term component is intended to be broadly construedas hardware, firmware, or a combination of hardware and software.

Some implementations are described herein in connection with thresholds.As used herein, satisfying a threshold may refer to a value beinggreater than the threshold, more than the threshold, higher than thethreshold, greater than or equal to the threshold, less than thethreshold, fewer than the threshold, lower than the threshold, less thanor equal to the threshold, equal to the threshold, etc.

It will be apparent that systems and/or methods, described herein, maybe implemented in different forms of hardware, firmware, or acombination of hardware and software. The actual specialized controlhardware or software code used to implement these systems and/or methodsis not limiting of the implementations. Thus, the operation and behaviorof the systems and/or methods were described herein without reference tospecific software code—it being understood that software and hardwarecan be designed to implement the systems and/or methods based on thedescription herein.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure of possible implementations. In fact,many of these features may be combined in ways not specifically recitedin the claims and/or disclosed in the specification. Although eachdependent claim listed below may directly depend on only one claim, thedisclosure of possible implementations includes each dependent claim incombination with every other claim in the claim set.

No element, act, or instruction used herein should be construed ascritical or essential unless explicitly described as such. Also, as usedherein, the articles “a” and “an” are intended to include one or moreitems, and may be used interchangeably with “one or more.” Furthermore,as used herein, the term “set” is intended to include one or more items(e.g., related items, unrelated items, a combination of related itemsand unrelated items, etc.), and may be used interchangeably with “one ormore.” Where only one item is intended, the term “one” or similarlanguage is used. Also, as used herein, the terms “has,” “have,”“having,” or the like are intended to be open-ended terms. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

What is claimed is:
 1. An apparatus comprising: a plurality ofwavelength selective switches; a plurality of transmitters configuredto: transmit a plurality of super-channels; a plurality of passive powersplitters, corresponding to the plurality of transmitters, configuredto: receive the plurality of super-channels, generate a respective setof power-split super-channels for each super-channel of the plurality ofsuper-channels, and transmit each power-split super-channel of therespective set of power-split super-channels to a correspondingwavelength selective switch of the plurality of wavelength selectiveswitches; a wavelength selective switch, of the plurality of wavelengthselective switches, being configured to: receive a plurality ofpower-split super-channels, of the respective sets of power-splitsuper-channels, from the plurality of passive power splitters;selectively route a portion of the plurality of power-splitsuper-channels toward a receiver; a plurality of combiners; and aplurality of receivers; another wavelength selective switch, of theplurality of wavelength selective switches, being configured to: receivea particular super-channel, selectively route a portion of theparticular super-channel to a corresponding combiner of the plurality ofcombiners, a combiner, of the plurality of combiners, being configuredto: receive a plurality of particular super-channels from two or more ofthe plurality of wavelength selective switches; combine each of theplurality of particular super-channels into a combined super-channel;route the combined super-channel to a corresponding receiver of theplurality of receivers; a particular receiver, of the plurality ofreceivers, being configured to: receive a particular combinedsuper-channel from a corresponding combiner of the plurality ofcombiners; and determine information being transmitted via theparticular combined super-channel.
 2. The apparatus of claim 1, furthercomprising: a substrate; and where the plurality of transmitters includea plurality of lasers mounted on the substrate.
 3. The apparatus ofclaim 1, where one of the plurality of combiners includes at least oneof: a power-combiner; a wavelength selective switch; an arrayedwaveguide grating; or a fixed passive spectral filter.
 4. The apparatusof claim 1, where the wavelength selective switch includes: an opticalfilter configured to: filter a set of optical signals associated withthe portion of the plurality of power-split super-channels from aplurality optical signals; and direct the set of optical signals towardthe receiver.
 5. The apparatus of claim 1, where the wavelengthselective switch includes: a port configured to: route the portion ofthe plurality of power-split super-channels to another wavelengthselective switch of the plurality of wavelength selective switches. 6.The apparatus of claim 1, where: a passive power splitter, of theplurality of passive power splitters, is configured to: receive aparticular super-channel of the plurality of super-channels, generate aparticular set of power-split super-channels of the respective sets ofpower-split super-channels, a particular power-split super-channel, ofthe particular set of power-split super-channels, having a transmissionpower proportional to a quantity of power-split super-channelsassociated with the particular set of power-split super-channels.
 7. Asystem comprising: a reconfigurable optical add-drop multiplexerincluding: a set of passive power-splitters connected to a set ofoptical transmitters; a first set of wavelength selective switches, eachwavelength selective switch, of the first set of wavelength selectiveswitches, being connected to the set of passive power splitters; a setof power combiners connected to a set of optical receivers; and a secondset of wavelength selective switches, each wavelength selective switch,of the second set of wavelength selective switches, being connected tothe set of power combiners, where a particular wavelength selectiveswitch, of the second set of wavelength selective switches, isconfigured to: receive a set of super-channels from a node of an opticalnetwork; route a first super-channel, of the set of super-channels, to aparticular wavelength selective switch of the first set of wavelengthselective switches; and route a second super-channel, of the set ofsuper-channels, to a particular power combiner of the set of powercombiners.
 8. The system of claim 7, where: a first wavelength selectiveswitch, of the first set of wavelength selective switches, connects to afirst wavelength selective switch, of the second set of wavelengthselective switches, and a second wavelength selective switch, of thefirst set of wavelength selective switches, connects to a secondwavelength selective switch of the second set of wavelength selectiveswitches.
 9. The system of claim 7, where: the reconfigurable opticaladd-drop multiplexer is configured to: receive a set of super-channelsfrom a source of the set of super-channels; route a first super-channel,of the set of super-channels, to a first node of an optical network; androute a second super-channel, of the set of super-channels, to a secondnode of the optical network.
 10. The system of claim 7, where: a passivepower splitter, of the set of passive power-splitters, is configured to:receive an optical signal from a particular optical transmitter of theset of optical transmitters; generate a set of power-split portions ofthe optical signal corresponding to the first set of wavelengthselective switches; and transmit each power-split portion of the opticalsignal, of the set of power-split portions of the optical signal, to acorresponding wavelength selective switch of the first set of wavelengthselective switches.